Continuity mistake: In season one, Sara is a brunette in Oliver's flashbacks. In this season's flashbacks, she's a blonde (most noticeably the ones aboard the Queen's Gambit).
Arrow (2012)
1 mistake in Season 2 generally - chronological order
Starring: Katie Cassidy, David Ramsey, Stephen Amell, Colin Donnell, Emily Bett Rickards
John Diggle: The knife.
Oliver Queen: Right. The knife. I got lucky.
John Diggle: That was a kitchen knife. It wasn't even weighted properly and yet you threw it with accuracy across a ten foot room.
Oliver Queen: Exactly. I got lucky.
Trivia: Although Laurel is a couple of years older than Sara, Katie Cassidy is only about a month older than Caity Lotz.