"So you have - a small amount of acid and some metal, in there, and these react in a way that... lights your rectangle?"

"Well, there's a large number of intermediary steps between the battery and the rectangle for other reasons, but making light's not that complicated, no!  If I knew what actually went into lightbulbs other than 'glass', 'vacuum' and 'some sort of high-electrical-resistance filament'...well actually, arc lamps came first and those you can do with just electricity and wire, plus a cover for safety, though they're kind of power hogs and also absurdly bright, I think."

He's gotten ahold of a notebook now. "Electricity being the thing that happens when you combine the correct metal and acid? In what proportions? What should the wire be made of, if it needs to touch the acid bath?"

"Copper and gold are good wiring metals, and there's the terms anode and cathode that - ugh, there's got to be something about which metals go where but I don't have the periodic table...Actually let me check if it's in my calculator!"

And it is!

"And those are fresh batteries!  So we have plenty of time to write them down!"

It transpires that they don't have the periodic table.

"Of course not, you meddle with things in ways that make even starting to think about fundamental properties kind of absurd; color's a property of electron orbitals and you just change it at a whim, y'know?  ...Zinc is ringing a bell for some reason...Anyway.  I think that if you stuck copper wires in a lemon, you'd get a shock.  ...You don't have the same vegetation at all.  ...You would probably know what works, though."

"I don't use troportation during experiments," he says indignantly.

"You in the collective sense of 'people around here', I mean.  Place I'm from didn't have it.  I'm really curious to see what happens when we do add troportation to our list of variables, honestly."

"What is the important property of a lemon?" he sighs.

"It has citric acid in it."

"Is that a particularly useful acid for the purpose?" Write write.

"Not as far as I know, but I don't know the commercialized sorts; it also really depends on your use-case.  Motor vehicles used lead-acid, which - by the way do you know that lead's brain-damagingly bad for you, and mercury's bad as well -"

"- mercury I knew, lead I didn't."

"Lead is unfortunately quite pernicious, and so otherwise-useful, as well.  It's really quite rude of the universe.  Sweeteners, pipes, paint, additive to fuels for some reason, sometimes it just shows up in groundwater - the fuel additive was definitely associated with statistical decreases in intelligence, our government, notoriously not fond of regulating things, passed one about obligatorily removing lead paint.  I forget precisely how or why it does the thing, but I have a vague guess of 'gets in your internal chemical supplies and then your body doesn't even know how to get rid of it', because lead poisoning never goes away, once you have it.  ...Speaking of dangers, do you have a word for radioactivity..."

"I'm... not actually aware of lead being used in any of those things. Or of 'radioactivity'."

"Good.  That's good.  It shouldn't be.  ...Radioactivity is a thing where sometimes the fundamental structure of big-enough atoms is unstable, so they spontaneously break down, and emit harmful byproducts, that're bad for the chemical instructions for making humans in your body, which sometimes can even make other stuff radioactive.  As well as usually leaving more and different unstable atoms behind.  Avoid pitchblende; I'm pretty sure it's one of uranium's ores, which is invariably radioactive, as well as having both radioactive and non-radioactive lead in it too.  Same goes with especially - so, light has a wavelength, like - I don't know if you even have tides, but light's.  Okay light's weird, unless you don't have quantum physics here, because it is both a wave and a particle and I think something about that explains why if you hold a prism to a sunbeam different colors spread out.  Anyway, really-really-high-frequency light, like, millions of oscillations per - small unit time I'll have to rederive somehow probably, is one of those byproducts of radioactive decay, and that's bad for biology-in-general."

"...Ironically, lead's really good at shielding people from that!  Enough that people used it for that purpose even in my time, anyway, though it might have been that other materials were in much shorter supply."

"- why were other materials in shorter supply?"

"They couldn't do troportation, there."

"- that must be ludicrously inconvenient."

"Oh, it definitely is, but we rose to the challenge.  None of what I have with me has been troported at all.  ...Except this shirt, which I changed the colors of a few times to see if troportation worked for me, now that I'm here, or if I needed to hide under the dreamward posthaste.  ...It didn't have the monsters, at least, despite...well.  People still finding reasons to do violence.  And they were mostly stupid reasons, in my opinion, but I think that line of thought is better saved for a historian or something."

"Oh, demons practically never make it into the city. Unless you count klaonso."

"Wouldn't know, what's a klaonso?"

"Singular is klaon. They're insubstantial, so the city walls can't keep them out, but they can't eat you so long as you're awake."

"...are they perceptible?  What happens when they try eating you?"

"They're pretty hard to see but sometimes you can make out a faint mist. It's just hard enough that you should never assume there isn't one near you, particularly since nothing's stopping them from drifting along underground. They eat souls like all demons, they're just special because they don't have to eat your body to do it."