Cats have a long-standing relationship with humans. They have been loyal housemates for several centuries. In general they weigh between 2.5 and 7 kilogrammes, stand just under 30 cm high and are 50 cm long. Cat's teeth, tongue and ears are highly developed, and they are able to express their mood through body language. Their set of teeth is that of a carnivore. Their tongue features little barbed papillae which help both to groom their fur and to spread their characteristic smell. The ears are capable of perceiving very high tones. They may trigger allergies, but are nonetheless one of man's best friends.