Revealing mistake: When Iris is sitting in bed recording the message for Barry, she is holding her iPhone so that the start button is on the left side, but the "video record" button appears on the right. Additionally, her right hand covers the speaker area of the phone fully, including the front facing camera. It is impossible for Iris to be recording the video live and reveals that the video footage was recorded ahead of time. The illusion that the video is being recorded by Iris live is further ruined by the fact that the room lighting is turned off in the scene, but the recording is well lit. (00:02:55)
Visible crew/equipment: During the final battle between Duncan and Luther, you can see a crew member holding a boom microphone pole standing on the stack of hay bales in one of the shots. (00:44:10)
Shelter from the Storm - S3-E18
Continuity mistake: When Winn and Brainy hug, Winn starts the hug with one arm high and one lower, towards Brainy's waist. The shot cuts and both his arms are up and in the centre of his body.
What Price Gloria? - October 16, 1961 - S2-E4
Continuity mistake: When Sam goes out of the window to save Gloria, part of the ledge breaks off, but in the near shots it is broken off almost to the corner near Gloria, while in the shots from below most of the ledge is still intact. (00:35:45)
Ashes, Ashes - S1-E6
Continuity mistake: Spoiler! At the end of the episode, after Elektra decapitates Alexandra, the blood pattern on her changes changes when she turns around and asks "any questions?" Most noticeably more blood on her forehead and two streaks down her chin that suddenly appear. (00:49:10)