A former colleague of mine keeps telling how she lost her CAE in an "accident". She had bought it as a "community-friendly algae eater" only to find out in time that it was neither friendly nor the least bit interested in algae. But the store she had bought it from no longer existed, and she didn't have the heart to just kill the fish. So, while figuring out what to do with the CAE, she kept it with a bunch of danios who were too quick to be seriously harassed by it.
So this one time after feeding the fish she had forgotten the cover of the tank open, only to hear a little "splat" after a while. She ran into the room, fearing for her danios, and saw two things: the chinese algae eater trashing on the floor, and her cat walking in from the other end of the room.
She decided she hadn't actually heard the little "splat" and left the room, and the CAE was never seen again.
That's how the story goes anyway. I always suspect she had a hand in making the accident happen.