Baby keys, plastic hoops and rings, fishing lures with the hooks removed, crayfish in one of those clear disposable salad dressing cups, plastic cat toys, crickets tied up over the water or placed in a clear plastic ball, laser pointer... I experiment with alot of different things. He also likes to steal my algea scrubber, swim off with it, and beat it up as if he just defeated a monster. That usually results in me yelling cuss words at him and him looking very proud of himself.
The baby Os like a glow in the dark ping pong ball that has a little bug drawn on it. They bop that thing all over the tank when the lights go out.
