Final answer:
David used a sword to cut off the head of the Philistine.
Step-by-step explanation:
David used a sword to cut off the head of the Philistine. According to the Bible, in the book of 1 Samuel 17, David famously defeated the Philistine giant named Goliath using a sling and a stone. After striking Goliath in the forehead with the stone, David used Goliath's own sword to behead him and prove his victory.