After Achilles's cousin has been killed, Achilles is challenged to fight Hector. On the fight, Achilles won and killed Hector, he tied Hector and dragged him until his camp. Look closely, when Achilles tied Hector and dragged him, there is a spear stuck on Hector's chest. When Achilles arrived in his camp, the spear disappeared.
More importantly than that. Where did the spear come from in the first place? In the angle shown from behind Achilles just before he stabs Hector with the spear, he is only carrying a sword and nothing else. Then the camera angle jumps, Achilles does his twirling thing and stabs Hector with a spear that seemingly came out of no where.