"I dissected a bunch of eyes! Because I have these dead bodies around anyway. But I don't know what all the parts do."

He is going to lie down and relax and be VERY obedient while Wen Ning takes notes. 

He dissected eyes! Because he had a bunch of bodies available anyway! That is bizarrely endearing. 

Merrin will cheerfully explain everything she can remember about how different mediums - air, water, glass, eyeball fluid, also vacuum although she's not sure if his world knows that's a thing? - have slightly different speeds of light, and if you model light as straightforwardly propagating as a ray (which is mostly true and she can get into things like diffraction patterns later) then the change in lightspeed causes the rays to effectively bend (or sometimes be reflected back, it's complicated). Human eyes, actually all mammal eyes as far as she knows, have a lens that can change shape via tiny muscles, to affect exactly how it makes the light bend. The iris also has muscles that change the size of the pupil and thus the total amount of light that gets in.

She describes how retinal cells, rods and cones, absorb photons of light - okay sorry she'll come back to the fact that light is both a particle and a wave LATER - and react chemically and then send a tiny electrical signal, which eventually reaches the visual cortex where enormous amounts of processing happen in order to convert the exact pattern of photons of various wavelengths (colors) hitting the retina, into an image of the world. 

This is surprisingly fun and also wow Merrin would need a lot more practice at this to be a good teacher. 

She pauses after five minutes or so to ask if Wei Wuxian is feeling less nauseated now and if he thinks he could drink more of the sugar-salt-water. 

Wei Wuxian has a lot of questions and he wants to know which of these he can test and also if light is a kind of energy does that mean you can cultivate with it like qi? He thinks he should invent multiple schools of cultivation. That would be cool.

Wei Wuxian is VERY nauseous but he can definitely drink some more sugar-salt-water.

Merrin is slightly worried that it's not great for him to be having a conversation where he's constantly compelled to ask questions and keeps forgetting the 'lie still' part.

On the other hand, at least she now has one (1) effective bribe to get him to listen to her. 

"- Yes, light is a form of energy! You shouldn't take my word for it, though, I can tell you what I remember about experiments you can run at this tech level. I mean, it could be different here, since it seems like other aspects of physical laws are." She honestly does not have the slightest idea if light being a form of energy means you can cultivate it??? 

"...It's pretty important for you to get more fluid intake, it'll help with everything, but if you're still nauseous then you should stick with one spoonful at a time and then waiting a minute." Merrin is confused and kind of concerned that he's still having a hard time tolerating even basic oral rehydration solution by mouth? ...She actually has very little sense of whether this is normal, though, it's not like her clinical experience involves very much at the intersection of 'patients who inexplicably failed to eat or drink for days to weeks' and also not having access to any BASIC NORMAL EQUIPMENT AND SUPPLIES. 

She folds one of the blankets into a square and uses it as a pillow to prop him up against her folded knees, so he's still mostly reclining but upright enough to drink. She gives him a spoonful. "- All right, I'll tell you about what tests you could run, but first I want you to tell me how long it's actually been since you ate anything. I want you to try really hard to remember." 

"...does wine count?"

The translation magic effect is helpfully - or perhaps unhelpfully - unpacking that as "grape" "alcohol" which is such a baffling combination of concepts! 

"....I - on reflection - should have asked more questions when you mentioned getting in trouble for sneaking out to get 'alcohol'. I thought you meant– actually I mostly didn't try to interpret it because I was distracted by other facts about your world, but I implicitly thought you meant for, like, cleaning things? But it sounds like you maybe meant for........drinking."

Merrin is now retrieving some long-ago-memorized facts about chemicals and their known psychoactive effects. She - does not have fewer questions now! 

"....I confess I am still very confused about why but - if I'm not mixing it up with some completely different random chemical substance that people where I'm from do not normally consume then I think it has diuretic effects as well as, um, mental effects that I'm not sure why anyone would want. So I think that might manage to be actually worse for hydration than not drinking anything? ....I guess it has any caloric value. I think? I'm actually not sure. Either way I am going to declare that no that does not count. When's the last time you were eating or drinking anything that wasn't grape alcohol." 

"Mistress Dath, you should get drunk and then you'd know why people would want it. a-Ning get her a jug."

"I am really dubious of that actually! Also I am super not inclined to test the effects of weird chemicals on my brain while I'm busy trying to treat you. Also you still didn't answer the question." 

"I-- think I had some food when I was meeting with the Jin before I told them that if they didn't give me Wen Ning back I would tear them all limb from limb?"

He wishes that instead of being a thing that happened this was a thing that didn't happen. 

Oh no it's another topic that's likely to make Wei Wuxian very upset and angry. At least he's already mostly lying down? 

She really wants to give both of these poor children a hug. And then fix their entire world for them.

–huh where did that thought come from. That....is not the sort of thing that Merrin thinks of herself as being even slightly capable of. Though it's not as if she had any previous reason to wonder about that, really. Dath ilan didn't need fixing. It was fine. Better than fine, really. 

...Merrin isn't sure if she can be okay, though, if she's in a place where entire families murder entire other families for, as far as she can tell so far, no discernable reason. Where people's homes are burned to the ground and children die in the process. Whether or not they have 'souls', that preserve their mindstate and information and personhood, so they can be - vengeful, angry, lost ghosts. Or so that they can - come back again and start new lives, over? She didn't really follow that part. It's...better, she supposes, than the alternative. But it doesn't feel like it makes it okay. 

One of her hands is occupied with the container of rehydration solution, but she puts the spoon back in it and frees up an arm so that she can reach out and take Wei Wuxian's wrist again to check his pulse. She wants to know if his heart rate is spiking to unhealthy levels again, but also it gives her an excuse for some semblance of comforting touch. 

She doesn't say that she's sorry. It's pretty understandable, that it doesn't help. 

...She can't fix it. She can't undo any of what already happened and it's unlikely she can do much for the next few weeks - or months, or maybe years - either. 

But she can show them how to make planes. She can teach them the math to understand the fundamentals of their reality, even if she has to fight to dredge it up from long-ago lessons that she barely understood at the time and hasn't thought about in a decade. 

- and if she tries very hard and applies all her hard-earned skill, and if the chaos of this world can hold still for her for just a few more days, then she can keep this kid, with his anger and curiosity and obvious brilliance and absurd inability to stay on topic for five seconds in a row and his walking corpses and his eagerness to be an exceptionally resentful ghost, from getting himself stupidly killed because he insists on making life choices like "only consuming inexplicably grape-flavored cleaning products". 

...She should probably, at some point, say something. 

"I don't know how many days ago that was," she goes with. 

"Uh. It was definitely a number. That is... more than one? I kind of lost track of time."

"Well, in future you should plan on not going more than one day without eating food and drinking fluids that aren't even slightly things that one would sanitize medical equipment with." She feels really bad asking the clearly-incredibly-traumatized other boy, who it sounds like was - kidnapped? or something? and maybe mistreated? - by this other clan, but maybe he'll remember it better, since he presumably hasn't been starving himself in the interim. "Wen Ning, do you remember how long ago this was?" 

"No, Mistress Dath, I wasn't here. I was reassigned to the Jin supply truck because no one else had a personal slave and zhuren didn't need one either."

"I'm winning their entire war for them, that's why I deserve a slave."

"Yes, zhuren."

"...Right. Okay. It's fine, it doesn't matter. We're starting from wherever we're starting, and it's not as though I'm an expert on exactly the difference between not eating for two days versus three days."

She sits for thirty seconds or so in silence, trying to let various recent pieces of information propagate. 

"...Wei Wuxian, I am kind of worried about the fact that you're still having such a hard time even taking fluids by mouth. This stuff is supposed to be good for nausea and very easy to absorb. I'm wondering if drinking lots of alcohol might've messed with your digestive tract more than just not eating would have. In which case I am maybe going to have to figure out how to improvise an IV and sterile fluids to give you directly into your veins in order to get you more stable and feeling better. I have no idea how, the exact concentration and purity is way lower-tolerance-for-deviations and as far as I know this world doesn't have plastic. ...If that word doesn't mean anything to you that basically confirms that, but I definitely haven't seen any." 

"I don't know what plastic is. I could probably invent it, though?"

"You probably could! I am reluctant to make a plan that depends on your ability to invent a new substance in the next couple of days while you're incredibly ill. I guess I can tell you what I know about how it's made?"

That seems like a safer topic than whatever happened to Wen Ning with the Jin clan. And she likes explaining science to Wei Wuxian. 

Wei Wuxian is totally going to sit still for EXPERIMENTAL medicine. That is the coolest kind of medicine. 

"We have needles for acupuncture, I don't know if that would help."

"I don't know what acupuncture is. Are they hollow? The kind I would use are hollow, and need to attach to some kind of receptacle that can be squeezed or shrunk somehow, because they're for injecting fluids or drugs through. ...And actually usually for an IV the part that stays there is plastic, but I don't know if that's absolutely necessary. You need a hollow tube, and a bag for the water - which has to have a very exact concentration of salt, in it, if you inject someone with a bunch of pure water they will die. If you inject someone with a bubble of air they will also probably die, although it takes than most non-medical people in my world think... Um. Anyway. Plastic is...made of petroleum products, I think? Or now some of it is made with plant oils because you can farm those, but originally. ...Does your world have rubber? I think that's from a tree. I don't know if your world would also have that tree, but rubber is - springy and stretchy?" 

At intervals of about one minute she will feed him a spoonful of rehydration solution, which isn't ideal - at this point she's putting about four in ten odds that he will at some point throw up again - but she's struggling to make any headway at all on getting him more hydrated, his pulse is still thready and too fast and his extremities are cold and when she gently pinches a bit of skin on his forearm it stays tented up and only slowly subsides. 

...She's scared for him. For both of them. She doesn't really know how seriously to take Wei Wuxian's pronouncement, that he's winning the entire war for them, but - it's possible. She can weigh up her estimated probabilities for a range of scenarios, of just how loadbearing he is to holding everything here together. 

(She so, so badly wants a prediction market with experts feeding in all of their much better predictions, throwing dozens of smarter, more appropriately-trained minds at turning this sea of chaos into something where she can make sense of what might or might not happen before tomorrow. She desperately wants just fifteen minutes with a Keeper to ask her most pressing questions.  She wants to not be alone. She wants a break from being the one in charge, the one who has to track everything that's happening and weighing up probabilities and priorities and plans, to appear calm and collected no matter what because the people around her are scared, angry, traumatized children. She wants to go home   she wants her mother  she wants a night tied up in a volcano lair where she will not have to make ANY MORE DECISIONS ) 

She can do this. At each moment it's just one more thing, one more task, one more decision, one more step, and she's not going to stop. But she wishes it was....less than this. 

"We have rubber. A rogue cultivator showed me a ball he'd gotten in the Americas made of rubber. I don't think we'd be able to get it in a very short amount of time, though. --We burn petroleum to heat water to make salt? I don't think they know how to do anything except burn it, though."

"Great! Um, if you want to make plastic with it instead of burning it, the first step is refining crude oil - I think the simplest way of doing that is distilling it by heat, you put the crude oil in a tall cylinder-shaped container and heat it gradually, and the lighter compounds will rise to the top and then hit their boiling point at different temperatures, and you can recover and condense the vapor and then you end up with a bunch of different piles, of various molecular weights. I....am not sure I remember which ones are used for plastic feedstock, but I think several in the mid-range work... Um, and then you need to do a chemical reaction that I think is called "cracking", and involves heating it at high pressure with no oxygen - no exposure to the air, sorry - and then it's ready for you to polymerize it, which is basically making all the little hydrocarbon chains stick together into much longer repeating chains, you need a catalyst for the chemical reaction...I am pretty sure at one point in my life I knew what some of the catalysts are but that was a long time ago, I'll try to remember...." 

Merrin will keep expounding her best guess at how plastics are made and occasionally managing to retrieve other helpful facts. She can feed Wei Wuxian fluids mostly without pausing. She would like to get all of it into him, but she's also paying attention for signs of tiredness. He's behind on sleep as well. (Unfortunately, it seems like bribing him with interesting science is maybe not as helpful for getting him to sleep?) 

"I think," Wei Wuxian says, "I might have a little trouble doing that in the next three days."