I started chopping and paring wood out with a small chisel.

The ball is the tricky part, but I just eyeball it and try to make it round. The circle drawn on each face helps a lot.

I'm getting close to finishing it.
I ran out of time, but hopefully I'll have more time soon. I'll whittle the ball a little smaller and then use a pen knife to break it loose from each corner. Then it will roll around in its little cage, and people will wonder how it got in there.