I got to swim with dolphins in the Bahamas a few years ago and it was such an amazing experience!  I remember watching one of them playing catch with a trainer and then playing a game with a cat who was hanging out on the dock!  I watched the cat bat a ball into the water and the dolphin kept bringing it right back.  I knew they were smart animals, but this is just cool... this dolphin in the wild knew how to ask a person for help!