The sound produced by a bull is known as a bellow. In bulls, bellowing indicates stress and hostility. Other indicators of hostility include kicking, butting, walking the fence, and assuming a variety of body positions.
One must never turn their back on a bull. If within 20 feet of the flying zone, the individual should proceed carefully. Rapid movement encourages pursuit. The most effective method of self-defense is to retreat gently to safety while facing the bull. In rare circumstances, a bull exhibiting a demonstration of aggression will retreat and turn aside if the opponent walks at least 20 feet away.