I recently made a few spherical containers with bayonet locks (twist&click) and typical ball sports design (like soccer), including a golf ball, which required placing a lot of dimples more or less evenly around a sphere (here's a video on this, which came out shortly after I designed the golf ball…). 

I also recently designed a quite spiky cylinder that is supposed to stimulate a bit of harmless pain, which under certain conditions (like ADHD) can help to focus better. It has a lot of spikes placed quite evenly….

Thus I though I might as well combine both ideas, a lot of spikes (492 - the golf ball had only 362), placed more or less evenly on a spherical container, to stimulate some nerves. If you don't press hard, it's more like a massage ball.

Printing:  Print two halves and one ring. I used a 0.4mm nozzle and 0.17mm layer height.

Assembly: Place the ring into one half, place the other half flush on top and turn it clockwise until it clicks twice to lock both bayonet locks. Opening and closing requires only one click, the ring is then still attached to one half. If you twist further to the second click, the ring can fall out. If you find that annoying, you can glue it to one half. Due to the spikes, this all might feel uncomfortable though.