Other mistake: When Linc sees the company is following them in Panama, he gets into a fight with one of the company men. During the fight scene, you can see a stunt double was used for it. You can see the stunt double's face for multiple seconds. (00:21:00 - 00:21:40)
And Then There Were 7 - S1-E11
Visible crew/equipment: Cherry pickers and lights are visible in front of the main entrance. (00:31:59)
Continuity mistake: You can see David with his hands behind his head, but in the next shot he still has his hands beside him, and only later places them behind his head. (00:34:48)
First Down - S2-E4
Continuity mistake: The front licence plate disappears from Link's car as it hits the tree. (00:03:20)
First Down - S2-E4
Revealing mistake: Throughout the entire car chase, you can see through the front window of both cars, including as Linc and Michael are run off the road. However, when the car gets airborne and hits the tree, the glass on the windscreen is now frosted up, so you can see no one is in the car when it hits the tree. (00:03:10)
First Down - S2-E4
Revealing mistake: During the car chase at the beginning, there is a shot of the cars speeding off just before we see the truck approaching. However, look carefully and you will see the truck parked up, waiting to move. (00:02:40)
Riots, Drills and the Devil: Part 2 - S1-E7
Continuity mistake: When T-Bag is talking about acne, the way he holds the picture of Bob's daughter changes between shots. Note his index finger. (00:29:10)
And Then There Were 7 - S1-E11
Continuity mistake: The severity of Quinn's wound changes throughout the episode. (00:04:00 - 00:39:30)
And Then There Were 7 - S1-E11
Continuity mistake: When Michael goes through the wall for the first time, he lifts the grate and his hand is in the middle of the grate. When the shot changes, his hand is now at the edge of the grate he is moving. (00:11:10)
Continuity mistake: When Patterson brings the tray to Linc at the start, the position of the milk on the tray changes between shots. Note the corner of the tray. (00:09:40)
The Old Head - S1-E8
Continuity mistake: Michael hands out sledgehammers at the end and passes one to Abruzzi with the head facing down. Abruzzi then passes this one to Lincoln but the head is now facing up. (00:39:00)
The Old Head - S1-E8
Continuity mistake: Bellick visits Westmoreland in his cell and puts his cigs in his pocket as he walks into the cell. When he sits down, he puts the packet away again. (00:25:40)
Riots, Drills and the Devil: Part 2 - S1-E7
Continuity mistake: When we see a military truck driving onto the grass at the start, it is by a white patrol car. When the shot changes to a ground level shot, the patrol car has gone. (00:03:10)
Riots, Drills and the Devil: Part 1 - S1-E6
Continuity mistake: We see Sarah banging on the window of the sick bay at the end. When she does this, she is banging with one hand and resting her other hand on the glass. The hand that is on the glass changes position during instant cuts. (00:41:00)
Answer: Because of coincidence.