Knex baby rattle.
Well, my nephew C***** (He's about 6 months) came over, and he was a bit fussy. So I wanted to make him something to keep him occupied, but it had to have no small parts. So I made him a little rattle thing. You can't get the green rods out without taking the whole thing apart. Which is really difficult.
I'll also try to incorporate it into a "noisy ball machine" I'm going to make.