Human speech differs from the cries of other species in many ways. One very important distinction is that all other animals use one call for one message as the general principle of communication. This means that the number of possible messages is very restricted. If a new message is to be included in the system, a new sound has to be introduced, too. After the first few tens of sounds it becomes difficult to invent new distinctive sounds, and also to remember them for the next time they are needed. Human speech builds on the principle of combining a restricted number of sounds into an unlimited number of messages. In a typical human language there are something like thirty or forty distinctive speech sounds. These sounds can be combined into chains to form a literally unlimited number of words. Even a small child, who can communicate by only one word at a time, uses a system for communication that is infinitely superior to any system utilized by any other animal.