Continuity mistake: At the dinner scene, just before Peter asks his mother if she's okay, the meat on his plate, (apparently chicken) is sitting with the mounted end up. It cuts to his mother then back to him without him moving, and suddenly the meat has flipped upside down the other way. And it flips around several times through this scene. (00:56:55 - 00:58:00)
Continuity mistake: In the classroom when Peter is being possessed, he slams his face down into his desk twice, splattering blood onto it. After he falls back screaming, the camera changes angles and now his desk is clear of blood. (01:38:25)
Answer: Earlier in the film, Peter swerves the car to avoid hitting a dead animal in the road, resulting in Charlie's decapitation. That animal appears to be a goat (a ram) with slightly curled horns. Within the context of this movie, this is probably a Sabbatic Goat, alluding to Occult symbolism associated with the Mystic Pentagram and the Satanic deity Baphomet. The implication is that Satanic forces caused Peter to swerve off the road, killing Charlie in preparation for migrating her soul into Peter. The dead animal seen in the background at the end appears to be the Sabbatic Goat again, marking completion of Charlie's soul migration into Peter.
Charles Austin Miller