Revealing: In season 4, episode 13: Pictures of You, Haley's pregnancy pad is visible when she raises her arms while lying on the table.

Deliberate "mistake": After the party, in the scene where Lucas goes into the cafe, he finds Haley crying. The shot is a distant shot with Lucas and Haley in it. Haley's hands are covering her face. In the next shot, just of Haley, her one hand is over her forehead.

Continuity: Haley's lipstick gets noticeably thicker and thinner between different shots when she's talking to Nathan (when she drops over some groceries).

Plot hole: How in the world could Keith be hired as a teacher? Not only is he a college drop-out with no teacher training, Dan mentions just an episode or two earlier how Keith is incapable of using modern machinery (specifically saying how every high school graduate will be more qualified than Keith).

Continuity: Throughout the entire episode, Lucas' hair length ranges from being short to long.

Factual error: Early in the episode, Lucas is listening to his Ipod on the river court. Later, Keith comes to his house and tells Karen that Lucas left it in his truck.