Bared teeth is a threat signal and is an integral part of aggressive biting. The amplitude of a bark is highest at the beginning of the sound and falls sharply thereafter. The pitch is usually between 2 and 3 kHz. Barks appear to be both threat and alarm calls, having a high arousal effect on other pigs, particularly preweaned young. Other animals react to barking with quick orientation, followed by a brief period of immobility and silence.
Behavioral symptoms are difficult breathing, repeated barking sounds, and uncoordinated locomotion.
Battery cages usually are stacked in several horizontal tiers and most commonly are used for housing of laying hens. The number of hens housed in each cage depends on its size, but generally varies between 3 and 10 birds. Since the beak is innervated, the ethical validity of beak trimming has been questioned.