prints without support! cat_toy_a: screw structure inside. Put some piece of catfood in and give it to your cat. cat_toy_b and cat_toy_c: while printing, add a steel ball (10mm .. 15mm) in the thing. Print without support because the slicer would fill support material inside. Stabilize the thing to printbed after z=20mm by using some glue or ABS-juice because of poor footprint. _b and _c have very small holes in one side because openscad cannot process hidden cavities. important: check if your slicer provide option "avoid crossing perimeters". Older versions of slic3r have this option button but it does not work. I use version 1.2.9 (Linux), this option affects something but not in a good way.