Then said David to the Philistine, You come to me with a sword, and with a spear, and with a javelin: but I come to you in the name of Yahweh of hosts, the God of the armies of Israel, whom you have defied.
It was a trophy that David had, and he wasn't gonna let the thing go. He was gonna carry it around for a few days. Must have been a big head too, you know, the guy's nine foot, six inches tall.