Maybe I'm just dumb, but I can't get mine to work!

The little piece in the center just slides in and out and anytime the keyrings move to the center, they fall out. No instructions with it, and nothing on Bison's website.

This is one of those, "well, maybe there are such things as stupid questions", questions, but I'm asking anyway. I don't even know how I got the center piece out because I was distracted by children, then the next thing I know, I've got keyrings falling all over the floor.

Help, please!