I had a foster that would play fetch. We used to say he was our dog until we got a real one.

His favorite practical joke to play on people was to get them started playing fetch, then he'd sorta disappear with the paperwad for a while. All of a sudden he'd come back with it and drop it at our feet, ready to play again. When we'd pick it up, we'd be grabbing a handful of soggy paper. I swear there were times I heard him giggle. After a while we learned to use paper that didn't soak up so much water.

He also liked to sit and watch ice cubes melt in the water dish. Ever so often he'd bop one of them with his paw and watch the water. We always wondered what was going on in his head - was he contemplating the molecular changes taking place in his water dish or was he waiting for the ice to melt so the cubes wouldn't hit his nose? Or was it another practical joke he was playing on us - what was stupider than a cat watching ice melt? Human watching a cat who's watching ice melt.