Most people know of the Karen people from television and magazine documentaries. The women who wear these brass rings on their neck belong to a sub-group of the Karen tribe known as the Padaung.
There are different accounts of why the Padaung practice this bizzare custom. Their own mythology explains that it is done to prevent tigers from biting them! Others have reported that it is done to make the women unattractive so they are less likely to be captured by slave traders. The most common explanation, though, is the opposite of this - that an extra-long neck is considered a sign of great beauty and wealth and that it will attract a better husband. Adultery, though, is said to be punished by removal of the rings. In this case, since the neck muscles will have been severely weakened by years of not supporting the neck, a woman must spend the rest of her life lying down. According to Paul and Elaine Lewis in Peoples of The Golden Triangle, adultery and divorce among all Karen groups is extremely low.