Revealing mistake: When morphing, a "Net" appears over the Rangers, which their Zeo powers then morph them over. Tommy and Tanya's nets don't match their bodies - for example, their shoulders aren't in the net, yet they disappear when their Ranger costume appears.
Revealing mistake: The orange soda cans are supposed to be full but when they fall they are obviously empty.
Revealing mistake: Throughout the entire series there is one staircase upstairs and two downstairs. And, they more than likely are not the same staircase because the two downstairs are on opposite ends of the house.
Revealing mistake: It is very easy to tell when Salem is a real cat and when Salem is a robotic cat.
Blue Wants to Play a Song Game - S1-E14
Revealing mistake: After Blue and Steve play the monkeys jumping on the bed game with the sock monkey, when the mail time song plays Steve gets up excitedly and his arm and hand get cut off.
Timberly Loves Arnold / Eugene, Eugene! - S5-E22
Revealing mistake: Timberly Loves Arnold: When Lila tells Arnold that it's sweet that he is hanging out with Gerald's sister, the stripe on her shirt is layered over her gold button for one frame. (00:05:33)
Episode #1.2 - S1-E2
Revealing mistake: Towards the end of the episode when Dinah, Lloyd and Harvey are walking to school you can see a man and a woman stood at the end of their driveway watching filming. (00:19:28)