Yo Karr was a giant eel who was given sacrifices by the Cavemob shrew tribe, as they believed that otherwise younger eels or "elvers" would not return as a result. It lived in the water in the Cavemob's cave.
A sacrifice was determined by walking under a stalactite; if water dripped from the stalactite onto a shrew, that shrew was the victim. Yo Karr was slain when one of Bodjev's daughters was the intended sacrifice. Tagg went into the lake and fought with it; he bit into the eel's neck and proceeded to stab it with the blade of Sawney Rath. As it had consumed many members of the Cavemob, the tribe did not bake it into pies like they had with previous eels; instead Yo Karr's carcass was rolled into the water where it had lived.