"How much does it cost to fix a broken bone?"

Well, he can quote her a number in a currency she's never used before. "...Or, hm, it's less than the power I'd draw after one shift, it costs more than you could make spinning for a couple hours, it doesn't cost so much that I know anyone who's ever just left a bone broken because they couldn't afford healing."

"What are shifts - like -"

"It really depends. You take anything you need down to the inner sanctum - I think sometimes non-mages imagine thumbscrews but first of all you want something cheaper to heal and second I actually mean, like, a flask of juice and a change of clothes. As you get closer it feels increasingly magical - which is unpleasant but kind of a mixed blessing, it makes violence more appealing and some people are squeamish - and on the way you ask yourself one last time who you want to be. So you have something in mind, so you know what you're trying to patch while the magic is eroding you. You have your own favorite thing to do - almost everyone hates almost all the options but you can often find something you hate less - and you find a place to sit and you get on with it. I used to work alone - I'd go when it was convenient for me, stay as long as I wanted to stay, and not have to spend one extra second exposed to the magic. That way is more efficient but it's harder, in the moment. These days I go with a friend so we can be moral support for each other. Some people get off or read books or - basically anything you can think of that sounds like it might make the experience less bad is something someone's tried. You mostly leave other people alone if you didn't agree to meet them there - they're busy, you're busy, they might be handling something sharp or delicate and not take well to being distracted - and...  if you were going to find it unbearable you'd just end up exclusively taking cleanup shifts, so no one is regularly finding it unbearable, but I think it's almost everyone's least favorite part of the job. Some people are masochists but almost no masochists are into spending hours on end in the bleakest room in the world. I find it very easy to remember that my work is important and makes a difference for people, and that's very motivating, but it's not the same thing as having fun, and... I like knowing I'm strong enough to put myself through a sacrifice shift, but I don't feel like I get a lot out of knowing I'm strong enough to put myself through a hundred of them.

"Anyway, when you're done, you heal yourself, take a shower, go relax for a while. You get into a better frame of mind and then you ask yourself how your thoughts are different from before your shift - do you believe any new fact claims, are you making any new judgments? - and you ask yourself if what you believe is true and the judgments you're making are ones the person you want to be would make. Sometimes you notice something interesting and important while you're down there, and sometimes nothing happens, but usually your thoughts get warped and changed and you need to set them straight. That plus relaxing plus the shift itself plus getting ready for it usually takes most of the day, especially because - healing is a fixed cost, so if you want to do overtime, you usually do it as part of a shift you were doing anyway. So I guess the short answer to what shifts are like is that you will spend the entire time thinking 'aren't I done yet?'"

"I thought being blind and deaf was supposed to keep your mind from changing?"

"Any way you can sense the magic at all is dangerous, it's just the difference between 'it takes some work to bounce back after a few hours of it' and 'in thirty seconds it will be questionable whether you're even the same person.'"

"Oh.

Why does it do that?"

"Unintentionally, we think. I am aware that that answer sucks and I too would like a more useful one."

"I hope they let Sing figure it out."

"That is probably the best argument for contacting Sing I've heard so far."

"It seems like it's like - net helpful, so probably there's some way it could be better - especially if it just doesn't understand very well -"

"Yeah, it's never actually betrayed us. And - it used to accept any sacrifice of the right amount of pain, so we know it can, but it doesn't anymore. It won't accept it unless it's self-inflicted or you don't flinch at all - not if there's even a hint of a struggle. And it can lend power to people irrespective of how much they've generated - it can do loans and to a certain extent mages can sell each other power - and it's not trivially obvious how to draw on it, you have to learn that - but it won't give you anything if you've never sacrificed, and if you stop sacrificing entirely it'll eventually stop giving you anything. So you can't have slaves that you torture and never explain the situation to, not as a technical limitation but because the magic won't let you."

"And it's okay for it to be masochists?"

"Yeah, it's tracking whether the sensation is - the bright noticeable intense one you get if you try to touch a fire, not how you feel about it. I'm actually thinking, Mars has more people and it's a lot cheaper for you to turn senses on and off, if you took the most trustworthy ten percent of Mars, and the half of that population with the most scientific aptitude, and the most masochistic third of those people, and offer them a cool job... what's one-and-two-thirds percent of Mars and what fraction of them would think it sounded like fun?"

"Probably some! I don't have a great guess and I'm not sure why you chose those numbers to begin with."

"Mostly made up based on a general sense that good mages are above average at the life sciences and one mage gone bad can do a lot of damage and if we had a flood of applicants and could get healing from Sing we wouldn't have efficiency concerns so I expect at that point anyone who's ever into any pain for any reason could just enjoy themselves. I could be completely wrong about how many people are even slightly masochistic or how much the average Martian knows about biology."

"People can get more masochistic! Like, over time carefully with drugs and exposure."

"...That is the trait I was least expecting Mars to have a way to just arrange for everyone to be better at."

"There are billions of people and some of them like developing new tastes! Or want to be more compatible with partners who have the opposite kink."

"I can see why you'd do it given the ability - are there other things you can change about people that I haven't thought of?"

"Maybe, but possibly not as many as you're thinking. Sing avoids directly acting on brains much. Bodies are easy though. Some people have wings and stuff."

"Huh. That does sound cool." He's not particularly interested but he's intimately aware of the problems they must have solved in making that happen and very impressed. "Why does Sing avoid that?"

"Back when it was first made there were a lot of things like it around at the same time. Some of them had a weird war, a lot of which was about figuring out which of them would win and agreeing not to have the war in exchange for something. It traded not doing brain stuff without a lot more confidence than it can easily get with one called Sugar Dream."

"...I have already lost count of the additional questions I have about that but - is just directly it more cautious about brains than other organs, or does it understand them less well, or are mistakes less recoverable or more unpleasant for the test subjects...?"

"Sing isn't written in a human language. Neither was Sugar Dream. I think Sugar Dream might have been worried about irrecoverable mistakes, but that's anthropomorphizing. They're not humans."