Mettaton very nearly finds out whether he can throw up, at that second 'suggestion'. Maybe the worst of it is knowing he's already done just that, given his torturer a little private show on the floor of the music room.

"...your creation?" He doesn't know what that means. Should he know?

He's never really spoken to Toshi, doesn't know enough to put any pieces together, and he's not thinking clearly right now, anyway.