Dolphins are very smart. But how they know who's who?
Scientists found out that there is a specific sound for each dolphin. That sound is their name. Scientists found some dolphins and recorded a sound from a dolphin underwater. They played it and listened very closely. Then scientists put back in the water and played the recording of their name. The dolphin with that name swam right up to them. So that is how dolphins know who's who.
Check out the video here.