Tried my best to translate, if someone's gonna fix it, go ahead, my japanese sucks anyway lol.

If it helps, the word she was looking for was "binbouyusuri", fidgeting.

Not sure how to translate the joke, though... but the way it is now isn't right (no offence meant).

I took a crack at making the translation fit the pun; the best I can do is have her screw up bouncing enough to get bumming. That sort of catches the original pun.