A similar dynamic goes on in coral reefs, where a small fish called the cleaner wrasse runs a health spa. Big fish arrive, and the wrasse picks parasites from their jaws, gills, and other hard-to-reach places. The cleaners get meals, and the clients get healthcare. But the cleaners sometimes cheat by nipping bits of mucus and healthy tissue. The clients punish them by taking their business elsewhere, and the cleaners themselves will castigate any colleagues that annoy potential customers.
