"Not really? Sometimes I want to know about what the subject would consider pretty. Also sometimes the brain is important enough to the surgery that putting someone to sleep wouldn't work well. Or I might get lonely during the surgery I guess."

"I can hang out with you if you wanna fix her eyes for the sun or whatever!"

"That should work, I think."

"Oh good. If it's gonna come by as often as the moon it'd be good if it didn't bother her."

"Yeah, the sun is once a day too."

Bonesaw can do the surgery later that evening, once Kat has fallen asleep on her own.

"Uh, she'll wake up from being just regular asleep if you start poking her a lot even if it doesn't hurt."

"Mhm, I poked her with a sedative first."

Eyeball slicing time! It is really rather surprising how much eyeball slicing can be done without detrimental effects, apparently.

If Beka has misgivings about the situation, none of them, at least, are about Bonesaw's ability to perform eyeball surgery that results in whatever she was trying to accomplish.

It's true - Bonesaw doesn't mess up eyeballs on accident. ... Well okay she's actually messed-up a lot of eyeballs on accident but they weren't her sister's eyeballs, they were eyeballs she was paying much less attentions to and cared a lot less about. 

"Can you hold these two parts apart from each for a bit?"

Hold!

Bonesaw goes to get some liquids. 

"Oh! Should I change the color while I'm doing this?"

"- well, I like her eye color the way it is but she doesn't have an opinion yet I guess."

"I could make them rainbow! Or change color with her mood! Or golden like the sun!"

"Huh, I guess mood eye color could be neat! What moods would go with what eyes?"

Hmmm... 

"Oh, I got it. A sort of ruby red for angry, goldish for happy, amethyst for when she wants a thing, silverish like the moon for calm, and maybe a few others?"

Bonesaw can send what she thinks they'll come out looking like.

"I like it! And black like she has now when she's... hmmm..."

"Bored or sad or uh, remembering the past?"

"I guess that works, it'd just be kind of sad if I never got to see her regular eye color again."

"I could make it default to it when she's not having a lot of strong emotions, or when she just wakes up from sleep. So it would be like the colors are being sort of pushed out by the emotions into her eyes, and when that doesn't happen the colors fade?"

"That's a lovely idea."

"Great! Also I want to have thee colors push outwards from her pupils across her irises, so when she changes you can get intermediate combinations of colors! Human eyes can do that sometimes and it's really pretty."

Bonesaw can send what this will look like!

"Wow, cool!"

Surgery time! This is going to be a lot more elaborate and she has to install some tiny little organelles into the eyes but not very complicated ones so they'll be ready by the time she's finished with the brain surgery portion of the emotion detection system.

Beka serves as surgical assistant as needed and sings to keep Bonesaw company when not needed.

"Huh." says Bonesaw after a bit, pinky deep in Kat's brain.