Reminds me of a David Attenborough documentary on dolphins. It was amazing - he acted out sign language on an underwater TV screen that trained dolphins promptly followed (i.e. put the blue ball into the red bucket).
After that, footage was shown of a country (escapes me which one at the moment) where the fishermen have had a symbiotic relationship with the dolphins for so long that when one dolphin gives the signal, the fishermen wade into the water, holding their nets in a semi-circle, and the dolphin group herd a shoal of fish into the waiting nets. The fishermen get a huge haul, and the dolphins get mouthfuls of the fish swimming away from the net! You have to wonder about how that started.
The third thing that amazed me on the program was an apparently recently developed fishing technique, where one dolphin (taken in turns) swims to the sand at the bottom of the shallows, and uses their nose to dig up and disturb the sediment, making it into almost a "wall" (the fish see it as such). It then herds the fish into the wall, frightening them into trying to jump over it - resulting in them leaping out of the water and into the waiting open mouths of the rest of the dolphin pod.
Did anyone else manage to catch this when it was on?