Animal psychology, taken in its most usual, broad, sense, refers into the study of the behaviour and mental life of animals other than human beings. It is synonymous with comparative psychology, but although the latter would be a more accurate term, it is less often used. Veterinarians sometimes use the phrase "animal psychology" to refer specifically to the study of disordered behaviour in animals. Animal psychology ought to involve the use of a comparative method, in which similar studies are carried out on animals of different species, and the results interpreted in terms of their different phylogenetic or ecological backgrounds. A Persistent question with which animal psychologists have been faced is the relative intelligence of different species of animal. Much effort has gone into explaining that this may not be a good question, but it will not go away. Indeed, some early attempts at a genuinely comparative psychology involved evaluating how well animals of different species could learn different tasks. Over the last few years a substantial body of knowledge has been built up about the psychology of animal behaviour.