Carnivorous plants. Specifically, Venus fly traps.
I decided to turn his old tank into a terrarium, with fancy strip lights and growth bulbs and all that stuff. I've had fly traps in the past, but I never had a proper terrarium for them, set up with the light levels they require. After I researched their needs, I planned to get everything purchased and set up, then bring home a fly trap.
While grocery-shopping at Meijer, there was a tiny, wilted, desperate VFT huddled in a dark corner, like a dog that's been too long at the pound. It had four shriveled leaves, one single green trap next to its black, dessicated twin, and its plastic pot of sphagnum was bone dry. It was the Charlie Brown Christmas tree of VFTs, and it cried out for love and attention.
So I brought it home. After a good drink of purified water and a tasty gnat, it's now sitting on my patio in full sun. Today I noticed it's sprouted two new trap buds, and it already seems to have perked up in general. I'm going to keep it outside at least through September, or however long before it starts to show signs of dormancy--apparently VFTs thrive better outside anyway--then either terrarium it over autumn (depending on how soon the temperatures drop), then put it in the back room until February.
*Sugar doesn't count as a caged pet; as far as time, money, and interaction levels he's more like a large house pet.