Most of the best rat enrichment costs nothing. Free and safe: cardboard boxes with doors cut in them, kitchen and kitchen-roll tubes, egg boxes stuffed with food and folded shut, paper bags, phone-book-style paper to shred, plain brown paper twists with a pea inside, and old (clean, holeless) t-shirts and jeans legs as tunnels. Cheap buys: cotton rope, willow balls, sisal, coconut shells, seagrass mats, unscented parrot toys and wooden bird perches. Rotate rather than accumulate. Swap a third of the cage furniture every week - the same objects in a new arrangement is nearly as interesting as new objects, and much cheaper. Foraging beats objects. A dig tray, scattered dinner, food frozen in a lolly, a ball pit with food in the bottom, or a puzzle feeder made from a cut-down bottle will hold a rat far longer than a plastic toy. Training is enrichment too: recall to a whistle, spin, hoop jump, fetch, and target training with a stick and a pea all work with rats and cost nothing. Safety check: no small parts to swallow, no loops or gaps that trap a foot or head, no rubber or soft plastic that can be chewed and swallowed, nothing scented, and no glue or staples. Replace cardboard once it is soiled.