Cribbing is a compulsive behaviour or stereotypy that is bothersome to many horse owners because of the damage it may cause to both the horse and the farm itself. While cribbing, the horse places his upper incisors on the surface of the object, flexes his neck, pulling against the object, and sucking in air. There are many beliefs as to why horses begin and continue to crib. Most believe that horses crib in response to boredom or frustration. Others feel these stereotypies are learned behaviours. While there is evidence of a heritable component to cribbing, studies have shown that very few cases are a result of watching other horses perform these behaviours. A decrease in gastric pH has also been shown to increase the frequency of cribbing in horses.