The Equation - S1-E8
Revealing mistake: The shots of Peter and Walter entering St. Claire's are recycled shots from the pilot. You can tell because their clothes change.
Fringe (2008)
1 revealing mistake in season 1 - chronological order
Starring: Joshua Jackson, John Noble, Anna Torv, Jasika Nicole
And Those We Left Behind - S4-E6
Plot hole: The very ending scene where Peter (in this version died in the ice as a boy so Walter's wife never met him) takes off some of the dust covers then picks up a toy airplane. The toy airplane he got as a child from ... Walter's wife when she was trying to placate him in an earlier episode for trying to run "home". This toy airplane wouldn't have been his as a child in this version of the universe. (00:42:00)
Phillip Broyles: Someone out there is experimenting, only the whole world is their lab.
More trivia for Fringe
Question: Why would Luke Dempsey be arrested along with his father? He had no idea what his father was doing, never aided him in any way and only found out the truth after catching him in the act.
Answer: He helped his father evade capture, impeding the investigation.