Revealing mistake: After Homer brings Santa's Little Helper home, Homer and Marge hug, and if you look behind them, the background is upside down. There is a picture hanging upside down, and there is a lamp which seems to be hanging from the ceiling. Then in the next shot, the background is normal. (00:21:40)
Revealing mistake: During the scene when the people at the pool think Chris is a car sitting on the diving board, just before Lois moves out of the shot before the scene changes, her lips disappear for a split second. It's really fast but still easy to notice even without pausing or slow motion.
Revealing mistake: It is strange that the news coverage at the beginning of this episode is able to cover the story from all angles in such rapid succession: from the helicopter straight to the ground, then even a close-up of the goon atop the crystal mount Diamondhead traps him on.
Revealing mistake: When the van drives upstairs, you can see that it wasn't destroyed.