Sans remembers the leeches and doesn't like it at all. He keeps moving for the door, walking backwards because he doesn't want to take his eyes off the corpse and the hazmat suit blocks his halo from seeing a full view of the room.

"Are there a lot of things like you? Living corpses."

Or whatever. Corpses alone are still very unsettling to Sans; monsters turn to dust when they die. He's gotten more used to bodies than he'd like to be since arriving here, but he still doesn't like it. More importantly, he wants to keep it at 'things like you'. Not like Sans. He's not involved. He doesn't want to be involved.