Belmarniss doesn't know what sterilizing means - oh. These people don't have germ theory! This is very reasonable, it's a very recent discovery on Earth too, and it is also a place Tanya can help the locals a lot once she's in a position to properly demonstrate things and convince people (and take credit for it).

"Infectious disease is caused by very tiny lifeforms, many orders of magnitude smaller than can be seen, which get into the body and breed by basically eating it. The body has ways to fight them; inflammation, fever and pus are the most common side effects of the body fighting the disease. Disease normally can only get into the body via the nose and mouth, but it can also get into open wounds. Sterilization is anything that removes or kills the disease-causing tiny lifeforms. Boiling water works, heating metal to the same temperature for a minute works, alcohol and some rarer chemicals work. Washing wounds with clean water also helps because it can mechanically remove any disease lifeforms that just got in. The main way bandages help wounds is by keeping disease from getting in until the skin can regrow, and they need to be sterile or they're just packing the disease in. Whether any object has disease on it is very hard to tell, it originally comes from other people's breath and blood and spittle but it can stick around for a long time, so it's simpler to sterilize everything that comes in contact with an open wound. This isn't a complete theory of disease, some things are not infections and some things are airborne and some can stay latent in the body and flare up years later, but it explains most kinds of disease and all of the ones relevant to open wounds. ...mosquito bites also spread disease, avoid mosquitoes."

"...I don't have any very specific contradictory evidence to that spiel but I'm going to take that less confidently than you do anyway because you're from another planet, no offense. Prestidigitating wounds is cheap though. I don't think we have mosquitoes down here but there are certainly critters that are more disease-ridden than others. Admonishing Ray is a force effect, so it might be a good test for your shield."

"...you may well be right, but I think defense in depth is best. I don't want to rely on Prestidigitation alone since I don't know what exactly it does. Unless there have been large trials that showed Prestidigitated wounds are almost never infected, or something like that. The problem with mosquitoes is that they seek you out at night and the bite doesn't wake you up, and on my planet at least they can carry several horrible diseases you can't get any other way, but if they're not known for that here that's good."

Tanya thinks the germ theory of disease is very likely correct even if specific diseases from her planet aren't present here, because - it's frankly bizarre for convergent evolution to have produced humans (and pigs) on a completely alien planet. It's much more likely that either they were imported (by some meddlesome entity) or that this is another, even more diverged variant on Earth's own history. And in both of those cases, humans come premade out of cells with bacteria along for the ride. This is idle speculation, though, and even knowing for sure which is the case wouldn't help her in any concrete way... well, once she sees a world map she'll at least know if this is an Earth.

"Did you prepare Admonishing Ray today?"

"Anecdotally even very novice wizards who should be as squishy as random farmers get sick less often than the random farmers, which could be because of Prestidigitating stuff?" offers Belmarniss. "I have one Ray today, for emergencies featuring people who I'd rather not murder, I can prep more tomorrow. It'd be useful to have as a sorcerer but my second-circle sorcerer spell is Fox's Cunning instead. Which you might want to try, come to think."

"I might. Can you describe what it does again, in more detail? Does it have any downsides or known side effects or aftereffects?" The gloss Belmarniss gave on all her spells earlier indicated it was some kind of mental stimulant, and Tanya has several of those already (not counting her coffee and chocolate rations) and is very aware of recommended dosages and interactions and how you ignore them when you're fighting for your life, which she notably isn't doing.

"Fox's Cunning makes you smarter. There are three spells that affect mental abilities so we tend to think of them as three separate things, though it's not actually impossible for someone to be good at math and shit at languages and those are both cunning-oriented. People say you should be careful with the Wisdom one because sometimes it makes you have sudden realizations that you don't have time to think fully through within the spell duration and then you try to execute on them afterwards while you're dumber, but Fox's isn't like that, I dislike the comedown but it doesn't make me do anything silly. It just makes you sharper at its sort of thing for as long as it lasts."

Hmm. "What do you typically use it for?"

"Thinking about things - even if they aren't centrally cunning things I think it gives me a little more slack in other dimensions, though that could be wishful thinking - and it also makes my spells hit harder. Most sorcerers cast from Splendor but my line is cunning sorcerers so it works on my wizard and sorcerer spells."

"Alright. If you can spare one today, please use it on me so I can see if it helps me with anything in particular." It won't affect her magic but it could affect how she uses it, or something less expected than that.

"Sure thing. Now?"

"Maybe after I try it once I'll know better what kind of situation to set up where I could measure the benefit more concretely, but nothing's coming to mind right now, so now's good."

It's one of her very favorite spells. "Fox's Cunning."

Ooooh. It feels a bit like her mental (*) speedup spell without the physical part? Tanya thinks she can notice and react a bit faster like this, and mental reaction speed beats physical speed every time in mage combat. 

And her own spell seems to compound with it! This might not be entirely safe (read: ever tested before), but it feels incredible... for emergencies. For incredible emergencies. She slows back down.

What else to test? Mental math, because Belmarniss mentioned that. Yep, she's much better at calculations and remembering long numbers. This isn't hugely useful, because the calculations she needs to do are either performed by her orb or ingrained on the level of reflexes, but the latter do benefit as part of the general mental speedup effect.

This is certainly a useful spell, if very limited by its short duration. It might be best used for planning, if she had a tough logistics problem in front of her she'd certainly appreciate the boost, but right now she has nothing to plan except their journey. She will need to make very sure Belmarniss packs everything necessary so there are no more omissions on the level of 'we don't need an actual medkit', but luckily that is just a checklist Tanya is already qualified to apply, barring any unknown-to-her unknowns.

"It performs as advertised. I think I'd benefit in combat that stresses my mental reaction times or requires tracking many targets or casting many spells at once, but it's not such an enormous difference that you should prepare it unless we're expecting and planning for me to have a difficult fight."

(*) Tanya's spells have physical effects. The 'mental speedup' spell catalyzes several neutrotransmitters in her brain, faster and more precisely than normal brain biochemistry permits. It also removes enough metabolites and toxins to make it 'safe' to use for as long as a minute (this is the other reason her brain doesn't do this out of the box). She also has spells for other useful ways of abusing her body.

"I never prepare Fox's because I've got it as sorcery. For a while I didn't even have it written in my spellbook. You think it'd make you cast faster? Casting faster is a huge benefit, Haste is one of the best buffs there is at third circle and it wears off ten times sooner and it does making people faster and it doesn't actually let you get more spells off."

"When firing optical spells it takes time to charge each one proportional to the energy output, and against mages that tends to dominate. But if I have a hundred small unshielded targets and I want to hit them quickly at low power - and they're not bunched together - then it would help. This is a rather contrived scenario, to be sure, which is why I said it isn't an enormous difference. It would let me fire enchanted bullets slightly faster - I can't enchant them as quickly as my gun can fire them - but I'm hoping not to have to use many bullets. More generally, this would probably help with my mental reaction time, the part of deciding to cast a spell, and with flying because I'm constantly adjusting my flight spell, but I don't expect it to make a huge difference. If the spell is free because it's a sorcerer spell then go ahead and cast it, I'm just not claiming it should get the highest priority. The speedup might be as much as ten or fifteen percent but it's not being applied to the slowest parts of the process so it's not important in most scenarios. ...do you think a hundred small unshielded targets swarming me is a realistic scenario?"

"It's not a cantrip but all I can do with the slots is Fox's or casting my first-circles. There might be swarms of bugs like that."

"If I needed to clear a room of insects I wouldn't try to target them individually, there could be thousands of them. Any part of the swarm that's sufficiently localized I can shoot with a few wide-angle spells; if they're all over a big room I could try a small explosion for the concussion effect. The reason to hurry would be to protect you, since my shield keeps insects out; if possible I'd fly you back a little and then go back to deal with them with optics. ...what would you do with a swarm of insects?"

"Preferentially Fireball."

"That makes sense. You'll need to warn me to get out of the way. We'll need to game out all the likely combat scenarios and decide on tactics, so we can react quickly in the moment without confirming everything with each other."

"If you cannot tune your shield to handle Fireball then I won't detonate one with you in the way, I know how big they are."

A fireball that doesn't cover a whole room (or underground cave)? Is that even a real weapon?

"My shield will absorbs the blastwave impact. I can make mirrors to reflect heat but if I protect my face with them I'm blind so I can't just keep them up all the time. I could make a mirror that reflects heat and lets through visible light, but I'd need to be sure the visible light won't burn or blind me. If the spell's emission spectrum is exactly the same every time then I could measure it once, and then test it with a mirror and a target behind the mirror and adjust from there. But if your spell's magic catalyzes fire or causes damage directly in some other way, rather than being the same as explosive heat, then I don't know how it would affect me and should be conservative."

"...well, if we take long enough about preparing to set out I can show you one, but a Fireball won't blind you and if you're not in its radius you'll notice it's warm but it won't burn you either."

"If it has a sharp boundary like that it must be a magical effect. Or a magical effect containing an ordinary explosion, if it was designed that way to protect allies, but then you'd have a wider-area variant too. It's still a good idea for you to show me your spells ahead of time, if it doesn't lose you significant option value."

"...yes, it's a magical effect. It's a spell. I do not have an urgent need for my third circle slots on a typical day, I can spend one on a Fireball to show you."

"...Every spell is a magical effect. The effect uses the mana to achieve a physical result. If the result wasn't physical, it couldn't affect other objects. The distinction I'm drawing is between a magical effect here that creates a physical explosion that affects you over there, and a magical effect that happens over there and makes you explode directly somehow. I can't create magical effects very far from myself, so all ranged effects need a mediating physical force to be created next to the me. ...'very far' can mean between one and tens of meters, depending on the spell, but only some illusions reach that far and it takes more mana."