Continuity mistake: When Pete and Myka first get to Warehouse 13 and walk up, the football that flew at Pete is lying on the ground close to the open door. In the overhead shot, the ball is gone, but is there again in the next closeup.
Continuity mistake: After the crash, Myka helps Pete out of the wreck. There is blood on his shirt, which disappears when he sits down on the road.
Continuity mistake: When Pete shows Artie the vial of Myka's blood, he is holding it between his first finger and thumb. When the shot changes to the front, he is holding it between thumb and ring finger.
A New Hope - S4-E1
Continuity mistake: After Pete dies and Artie prepares to use the astrolabe to turn back time, Pete's body shifts position on the ground when the camera cuts away but nobody moved him.
All the Time in the World - S4-E19
Continuity mistake: In the Istanbul's Paracelsus lab scene, when Shaton enters the room, the half of the philosopher stone he has drops out of his jacket. But then Paracelsus finds it in his pocket. (00:36:00 - 00:37:00)
Continuity mistake: When H. G. Wells tells the lawyer to step in the primordial ooze, just before he steps in his pants are already covered in it. (00:28:15)
Continuity mistake: When Raymond tells MacPherson about Artie being released, the shot changes, and the screen changes from showing a tally of ~540 artifacts to ~340, and the images of the scrolling artifacts change as well.
Continuity mistake: When Myka pulls up to the warehouse for the first time, Lattimer's car is nowhere near where she parks, and it can't be seen when they are talking for a moment. When the door opens, however, we see both cars fairly close to each other, but if they really were that close, Lattimer's car would have been visible in the previous shots.
Continuity mistake: When Pete picks the items up off the floor, he picks up two red skeins of yarn and the brush that sets up the whole episode. However, when he stands up and puts the items on the shelf, he now has only one red skein of yarn and one blue skein.
Continuity mistake: When Myka's sister hands her the poisoned cup of tea, Myka holds it in her right hand. In the next shot the cup is suddenly in her left hand.
There's Always a Downside - S4-E4
Continuity mistake: When Myka and Jinks first see the trumpet player, the camera stays on him while he plays. At one point he plays a long tone and the camera shows him press the first two valves as if to change a note. The note he is playing continues uninterrupted however. While there are some notes that can be played with more than one fingering, changing valves in the middle of the note always produces a momentary interruption of the note, at the very least.
There's Always a Downside - S4-E4
Continuity mistake: Right at the end when Artie and Pete are talking, Artie is looking down into the bag holding the artifact. The shot changes to his other side and he is instantly looking up and into the distance.