Okay, that answer's almost everything Sans would have asked anyway, but...

"Synthetic tears?" Sans looks back and raises... well, if he had eyebrows, he'd be raising them. The sentiment still stands. He knows he shouldn't be surprised, and yet here we are. Yep. This was definitely some Stupid Shit. He goes back to the robot again. "... Welp."

The skeleton didn't exactly have the tools to fix a robot, but he could at least look at the damage, sure. He grabs a rolling chair from the desk nearby and sits himself in front of Mettaton's body.

"I dunno what makes you think I know how to fix these kinda things, but... ehh. Why not? I'll give it a shot."

Which is... partly true. Alphys was the engineer. Most of what Sans learned from shadowing his father was a whole other story. Still, he knew enough. Besides, Papyrus already told people that Sans liked "science fiction" (Alphys probably helped), and it wasn't unheard of for him to play occasional handyman.

"So this pops open...?"

Nevermind. That's rhetorical. He pops the manual release pretty quickly on his own.