In Celtic mythology, a joint-eater or Alp-Luachra is a type of parasitic fairy.
Behavior
The joint-eater is said to sit invisibly and consume half of its victim's food.
It is is difficult to get rid of the Alp-Luachra. In all the stories the method is the same: the patient is forced to eat a great quantity of salt beef without drinking anything, and is made to lie down with his mouth open above a stream, and after a long wait the Alp-Luachra will come out and jump into the stream to quench their thirst.