Continuity mistake: When the bomb under the bus is being defused, it's counting down and beeping once every second. We see the timer at 0:45, then cut to the face of the woman defusing it - counting the beeps when we cut back it should be on 0:45, but it's jumped up to 1:06. Camera pans down to her face, then back to the bomb, and it's now on 0:43, but going by the beeps it should be on 0:36. We cut away again for 5 more beeps, cut back and the bomb's only just ticking onto 0:41.
Continuity mistake: Season 1, episode 17, "The Man at the Altar". When Annie is getting dressed after sleeping with Crowley, what she is wearing, how she is wearing it and where her arms are changes between each shot.