The Great Egg Heist/The Feud - S2-E9
Other mistake: In the Great Egg Heist, when they arrive at the museum, Jimmy gives everyone shishkabob-shaped earplugs for Libby's scream. But in the next shot, if you look at everyone's ears, there are no earplugs. Also, in the next shot, next to Libby you can see Carl putting his hands over his ears. This is impossible because the pointy ends of the earplugs would stab Carl's hands.
Other mistake: In the episode with the Lake Monster, Miss Fowl and Sam get attacked, the Lake Monster crushes the boat, but when Cindy shows the slideshow the picture shows that they are getting rescued standing on a complete boat.
Safety First/Crime Sheen Investigation - S1-E12
Other mistake: During Crime Scene Investigation, Jimmy explains his costume to Carl and, while saying "Sherlock Holmes", his chin goes into his jacket. (00:14:38)
Who Framed Jimmy Neutron?/Flippy - S3-E14
Other mistake: Stormshuckle tells Jimmy he was able to get into his lab using DNA from Jimmy's spit that was left on a straw. Throughout the show, it is shown that Jimmy accesses his lab by scanning a strand of his hair, never his saliva.
Normal Boy/Birth of a Salesman - S1-E3
Other mistake: When all the school kids are meeting outside the school when the meteor approaches, some of the background characters appear twice in the same shot.
Other mistake: According to "Attack of the Twonkies", if music is played around them, they'll mutate into a monster. However, in "My Big Fat Spy" during the song "I Have The Ring", there is a twonkie in the room that is somehow unaffected by the music.
Crouching Jimmy, Hidden Sheen - S3-E8
Other mistake: When Sheen is about to fight Yoo Yee, Jimmy puts the kung-fu disk in the dance machine. During the break in the fight, Jimmy asks Cark to get him the kung-fu disk to put in the dance machine, but Jimmy already had it in there at the start of the fight.
Other mistake: After Cindy says yes to Jimmy's proposal, he jumps with excitement until he realises what he did and screams "no" very loudly. Cindy is walking several feet away. How did she not hear him?
