It's a rabbit.
2 seconds sound clip from the The Secret of NIMH (1982) movie soundboard.
You can hear this line at 00:09:46.411 in the Blu-ray version of the movie.
Quote context
[...]
- Medium. Make that fast. Very fast. I have to go now. Excuse me.
- Well, of all the silly nincompoops. You got yourself all worked up over a rabbit.
- You should've seen yourself.
[...]