Why on Earth? Hair chewing.
My girlfriend has the habit of chewing her long hair. When I was at school I remember being told this was a very bad idea. Is it dangerous?
Not so long as she can vomit. Chewing hair can lead to hairballs (the technical term is trichobezoars) forming in the stomach. These comprise somewhat disgusting masses of matted hair containing undigested food particles. If they get into the small intestine they can cause dangerous blockages, requiring surgery, but often they're vomited up before they get to a dangerous size. Rabbits, which can't vomit, are often killed by hairballs.