Food Fight - S1-E6
Revealing mistake: When Pudgy Pig is standing outside of the food packaging plant, a human hand can be seen sticking out of Pudgy Pig's wrist. (00:15:30)
Other mistake: While Sonic and Tails are locked up in old Spelunk's cage during the cave-in, right before the huge diamondius crashes on top of the cage, there's a close-up of Sonic holding the bars, and the color of his torso becomes the same as the background mid-shot. (00:13:40)
Revealing mistake: When Lois and Clark are checking out Lenny Stoke and Derek Camden on Lois' computer, you can see the computer screen showing the script for Lois in that scene. (00:07:40 - 00:08:20)