When Mr. Mackey is giving his speech in the school about Al Gore, when the camera pans to the crowd it also shows Mr. Mackey in the crowd standing next to the school principle, which means it's a reused shot from another episode.
When Al Gore is yelling "Why won't anybody listen to me!", behind him is a guy pushing a wheelbarrow. His hand is not attached to his body.
Al Gore says the only way to kill Manbearpig is by flooding the cave with molten lead; however, after the cave floods with water, he presumes that it must have killed Manbearpig.