Best Day Ever/The Gift of Gum - S4-E20
Revealing mistake: When Squidward says "I suppose if you haven't fixed my clarinet, the concert would have been a bust", Sandy's tail is the same color as her suit.
He's Too Sexy for His Fat - S2-E17
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. (00:07:20)
How The Elephant Got Its Trunk - S3-E6
Revealing mistake: The white around Papa's lips and eyes is slightly running when he is sprayed with water. however the white is supposed to be part of his real skin.
Revealing mistake: When someone suggests crying as a way to get the emperor out of Fry's body, he says 'that's a great idea', the emperor's face stays still on Fry's stomach, instead of moving in sync with Fry's body. (00:15:50)
Stalk Like An Egyptian - S1-E10
Revealing mistake: At the beginning when the Egyptian mummy puts the ring on his finger, the tip of the finger bends like a glove.