That's it. A housefly.
5 seconds sound clip from the Fun and Fancy Free movie soundboard.
You can hear this line at 01:03:26 in the Blu-ray version of the movie.
Quote context
[...]
- Go on, gimme somethin'. Anything!
- See? Mickey never misses a trick.
- Well, can you change into a fly?
- A cute, teeny-weeny, itsy-bitsy housefly?
- Aw, you don't want a fly. How about a bunny with long, pink ears?
- Ha. Well, of course, if you can't do a fly, why, uh...
- Because.
- Okay. A teeny-weeny fly. With pink wings.
[...]