[She actually kind of jumps, but to be fair, she's a lot more on edge than he is.

Not that it's really hard, to be more on edge than Sans.

Undyne frowns down at him, one hand on her hip.]

What's up?? My weapons are shot and I don't know where we are! [She gestures expansively with the other hand.] This isn't what weather usually looks like up here!!