Keep your cat fascinated with this design of a roll-around-and-chase cat toy that uses threading, allowing you to take the two halves apart and swap out treats or other objects inside.  

The two parts are designed so that they can be placed on their flat side in the slicer, and printed without supports.  I'd recommend setting the “Vertical shells → Perimeters” setting to at least 5, to make it a bit more durable.  

I've included the 3MF file I used that shows the settings I used in the Prusa Slicer, as well as the “gcode” for what I used to print the ones shown in the photos on my Prusa Mini.

Enjoy!