A couple of summers ago, we picked up a SKLZ Reaction Ball at a local sporting goods store:
It bounces in funny ways to help you train your hand-eye coordination.
We decided to make our own using the new mesh intersection operator in Madeup. A reaction ball is the union of one big sphere and six smaller ones along the cardinal axes. Thanks to libigl, I didn’t have to do any cleanup of the result before we printed it:
It doesn’t bounce like the original, but it gets its reaction when you turn off the lights: