Entering, then, somewhat unglamorously into the fray - if "fray" is the right word to describe a battle against a sleeping opponent - Perseus whacked Medusa's head off. At just that instant, the winged horse Pegasus, offspring of Medusa and the god Poseidon, was born from the bleeding neck. Then Perseus donned his special getaway gear and departed victoriously before Medusa's sisters could take their revenge. Though these sisters were immortal, Medusa clearly was not. She died when her head was severed, which required the special cutting implement given to Perseus by Hermes.