The
booty hole is an opening at the opposite end of an
animal'
s digestive tract from the mouth. It is used for expelling unwanted solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as bones; food material after all the nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; and
dead or excess gut bacteria and other endosymbionts.