Plot hole: Didn't Dexter ever notice the giant fire pit in the ant farm?
Suggested correction: This is more of a question than a mistake. (To be fair, I don't think questions were a feature yet back when this was posted.) No, he didn't. He only noticed the fire pit (and the colosseum) when he was inside the ant farm. It most likely just wasn't visible to him from the outside, or it was too small for him to see it.
The Aptitude Test / Oskar Gets a Job - S3-E9
Plot hole: Mr. Simmons asked that each student put their name on the test folders, but the folders already had names on them when he handed them out.
'Unmei no sentaku' mitaina - S1-E6
Plot hole: Akito's attack is point blank, on a ship part of a fleet with Distortion Field activated (basically, they have shields, like the good guys' robots). The explosion he causes is according to Ruri's damage report big enough that it managed to vaporize 80% of the ships they were facing, but his Aestivalis and the other 3 right floating nearby make out of it literally without a scratch. (00:05:10)
Plot hole: Kenan ends up out of the door when trying to persuade the robbers not to give. Surely with all the media attention, a camera would have spotted him, and his family would realise it's Kenan. (00:20:30)
Plot hole: The bedroom scene finds Robert sitting up in bed after getting home from the hospital with his upper thigh injury. If he really had a wound in that spot, there's no way he could sit like that.