A relatively simple cat toy printed out of flexible filament.
My cat absolute loves it:
 

Carefully remove every bit of stringing before starting to play with your cat!
Please keep in mind that you shall not let your cat play alone with this toy. For the case that you are worried about choking, there is a version where the bigger loop has a small gap so that there is no danger associated with this. Luckily, my cat never even tried to get her head into the loop.

Print instructions

This design only works with flexible filaments!

I recommend printing relatively slow with a constant print speed and disabled retraction, this works best with flexible filaments.

Carefully remove every bit of stringing before starting to play with your cat!
You do not want your cat to eat tiny bits of plastic. Please keep that in mind.