What sort of tank does it have? Ping pong balls, floating ducks (rubber duck), you could try airstones, fish on the other side of a divider depending on tank size? A mirror as said may work. What sort of environment does it have, bogwood? Gravel? Sand? Rocks? Does it sit an area where things walk past it's tank a lot, things like dogs, cats or people of course. Feeder shrimp could keep it doing something during the day as well, I wouldn't promote the use of feeder fish however.