> peter wrege: we're in kindergarten. we're just learning the very first few words. and andrea is going to help us put those words together. >> simon: and you say we're in kindergarten now? >> wrege: yes. >> simon: are we in the process of compiling the child's dictionary? >> wrege: even an infant's dictionary. ( laughs ) it's a very, very complex process because we can't ask the elephant, "what did you just say?" >> simon: but they can match elephant sounds with behavior they can see, and classify those sounds into distinct categories. can you tell me what some of them are? >> turkalo: well, there's these low frequency rumbles. it sounds like a big cat purring. and those are the... those are the vocalizations that help keep groups in contact with each other. there are protest calls. in newborns, you have a particularly very high cry. and when you hear it, you know it's a very, very young calf. ( elephant squeals ) and some of these big bulls, when they go into musth-- which is this sexual state-- they make a special rumbl