No surprise here: the bottlenose dolphin is typically thought of as the most intelligent non-human animal after the chimp and bonobo, and the more research we do, the more impressive dolphins become. They've been known to teach each other games and tricks, like walking on their tails or blowing bubble rings; they can use tools (dolphins off the coast of Australia learned to keep sponges over their noses to protect themselves from spiny but delicious urchins); they've been trained by the navy; they've been proven to understand at least some elements of the concept of numbers. However, it's difficult to measure the dolphin's intelligence due to its capabilities as a mimic. Is it learning, or copying? Who knows?