Kelly, a dolphin, was rewarded with fish by her trainers for bringing them litter and dead gulls to clean her pool. She began hiding fish under a rock in her pool and used them to lure gulls, which she then brought to her trainers to receive more fish. She even taught her calf the same strategy.

Not only do the dolphins understand the meaning of individual words, they also understand the significance of word order in a sentence. (One of their star dolphins, Akeakamai, has learned a vocabulary of more than 60 words and can understand more than 2,000 sentences.) Particularly impressive is the dolphins’ relaxed attitude when new sentences are introduced. For example, the dolphins generally responded correctly to “touch the frisbee with your tail and then jump over it”.