Barking, in addition to whining, howling and growling, is a dog’s natural means of interaction. Barking is characterized by a series of brief, sharp sounds, that have the tendency to differ little in tone or pitch. A dog’s bark can represent territorial defense, physical effort of prominence, or expression of some requirement. Typically, barking is "a way of communication caused by a state of excitement." Being a natural trait, barking is not thought about a behavioural trouble, until it is produced in extra.