What was the shank of lamb used for in the Passover?

The shank bone, typically displayed on the seder plate during Pesach or Passover, symbolized the sacrificial lamb. The blood from the lamb was supposedly used to paint the door and window frames of Jewish households to identify them to the angel of death when it slew the firstborn sons of the Egyptians, so that it would "pass over" those houses and spare the Jewish children.