It won’t hurt you, kids!
It’s a 2.5" diameter ball that looks like it’s made out of wood, but it’s actually made out of foam. That’s why it’s "falsa" wood, not balsa wood. You can buy it from Begum9.
It will hurt you, kids!
Just be sure not to use a real wooden ball, like he one above, from Premier Wood Products.
And for God’s sake…
Ironically, although I discovered a photo of the ball above and wanted to use it to illustrate a scary ball you’d never want to catch, it’s actually a special kind of tricky puzzle ball called a Singapore Ball. This one was made by Shawn Hermans from Smiling Frog Wood Studio:
This maple singapore ball incorporates redheart wood spikes which
expand when the ball is tossed into the air. Upon return into your
hand, the spikes retract safely into carved interior. Not only does
this turned piece have internal moving parts, its also one of the few
works that create sound when shook.
I believe the Singapore Ball was first described in the book Woodturning Wizardry by its creator, David Springett>>
– How to make a Singapore Ball, Woodturning>>
– Woodturner artist gallery>>