Haha, yeah they can do that sometimes. My old LMB looked like he swallowed a marble:
Easily one of the biggest personalities of all the fish I've taken care of. If I cleaned the glass with a cloth on the outside, he'd chase the cloth. He'd come out of nowhere to tell the invading cloth what he thought of it.
Man I miss him, he was an awesome fish. He lived for just over 4 years, I'm not sure what their natural lifespan is.