Many studies have shown that sows in crates exhibit behavior such as bar-biting, head weaving, and tongue rolling, indicating chronic frustration. When given the choice, pigs will relieve themselves far away from where they sleep and eat. Sows in crates bite the bars, chew even when they have no food, and press their water bottles obsessively, all reportedly signs of boredom. The "Post" (uncited reference) writes that a report by veterinarians for the European Union concluded that abnormal behavior in sows "developwhen the animal is severely or chronically frustrated. Hence their development indicates that the animal is having difficulty in coping and its welfare is poor." This behavior, such as bar-biting and other stereotypic behavior can also lead to other physical trauma, such as sores from frequent contact with the metal bars, and mouth sores from sham-chewing and bar-biting. They also show behavior that indicates learned helplessness, according to Morris, such as remaining passive when poked or when a bucket of water is thrown over them. A review by the Scientific Veterinary Council of the European Commission states that repetitive "stereotypical" behavior has been found in "every detailed study" of pigs in gestation crates, but not in any other housing systems examined. A 2004 literature review by animal scientists determined that sows in stalls exhibited more "stereotypical" behavior than sows in group housing, but that animals housed in stalls had lower injury rates and higher farrowing rates. Some studies have shown that "sow behavior has been shown to differ among housing systems; often it seems to be the non-housing component (i.e., direction of bar, other substances present) of the system that is responsible for the behavior displayed by the sow."