Moses then went to the Pharaoh and asked him to let the Israelites go. However the Pharaoh did not agree. Finally God inflicted ten plagues upon the Egyptians before Pharaoh agreed to release the Israelites. The last plague was the killing of all first-born, both human and animals. However, to save the Israelites, they were instructed to mark their doors with blood from a lamb, so that the avenging angel would see it and know to "pass over" that house.