An Elephant's Brain is roughly five times the size of a human brain, and although it is not nearly as sophisticated, it is in the top ten most intelligent animals. Although they don't have advanced eyesight, their sense of smell is unparalleled, and they have a remarkable range of hearing. Elephants are said to be capable of hearing sound waves well below our the human hearing limitation and "opens the elephant's spatial experience far beyond our limited capabilities". The phrase is proably an adaptation of an ancient Greek expression - The camel never forgets an injury - which became adapted to the Elephant in the early 20th century. But while the words 'never forgets and injury' were dropped from the phrase, they probably are key, because it is in the fields of kindness and cruelty that the elephant seems to show longevity of memory. And the fact that elephants live for so long - 50 or 60 years - propvides plenty of opportunity for the advanced memory to be displayed. They are particularly adept at recognising keepers who have shown them kindness or pain, and it is perhaps their ability to remember the smells associated with that person which prompts the recognition. Working elephants memorise a large number of commands given by the handlers and are able to recognizes many other animals and people.