Other mistake: The Time Expansion Helmet was supposed to allow Dexter to perform his 30 minute morning task in 30 seconds. Since this is the case shouldn't the cat have hit the fishbowl ages ago as time is not frozen.
Other mistake: In the closed-captioning, when Arnold and Gerald "touch thumbs" (and you hear that "sproing" sound), the caption says "[glass shatters]"
Monkey Fun - S2-E13
Other mistake: Season 2 episode 13 "Monkey Fun": Just before the enlarged Titano appears at the zoo, there is a family watching normal-sized monkeys in a cage. The family father (farthest on the right) has a drawing disorder with his eyes: their pupils look up and down, respectively, giving him a rather goofy expression.
Blue Wants to Play a Game - S1-E12
Other mistake: The jigsaw puzzle Steve and Blue help Shovel and Pail with has a picture of everyone playing musical chairs from the Mailbox's Birthday episode, but Steve suddenly isn't in the puzzle. He played musical chairs, so he should've been in the puzzle.
Ruri chan 'Kôkai nisshi' - S1-E5
Other mistake: Seen from behind, the HUD of the game Ruri is playing is missing the mirrored version of the score. (00:02:00)
Darkness and Light: Part 1 - S1-E11
Other mistake: When the Outcasts are launching boulders at the helicopters, they hit one that explodes immediately, and both occupants can be seen emerging from the fireball, safely parachuting to the ground. Even if they were able to jump from the helicopter before it exploded, their proximity to the explosion would have killed them before they had the chance to deploy their parachutes.