I volunteer at a shelter, and I'm looking for ideas to help the cats. I let them out of their cages a few at a time, pet them, brush them, play with them, clean their cages and litter pans and change their bedding. I've bought a fan for the room, toys and more toys, and a scratching post. There's gotta be more -- I'm looking for challenges for them, that sort of thing, something for them to DO. Help!