How do you kill Furies?

Furies acording to ancient mythology where killed by dicapitation but no one was supposed to kill them because they where in charge to punish all souls who where evil during life time.

Once Zetes and Calais, the sons of Boreas, almost accomplished this, but Zeus' messenger, Iris, goddess of the rainbow, warned them not to slay the 'hounds of Zeus', even swearing by the River Styx, therefore 'making the oath most gods dreaded', that the Furies wouldn't trouble the wise king Phineus in Salmydessus.