After the fight in the canteen Danny was dragged away by the guards, seen wearing laceless shoes. But in solitary he is seen wearing sneakers with laces, something that would not be approved in such a place.
When 'Nitro' is bundled into the back of a prison van, he knocks a guard's hat off. As the prison van doors are slammed shut, the guard's hat is still firmly on his head.
In two scenes immediately before he is asked by Danny, whether he wants to play with them, the monk can be seen participating in the training.
Flipped shot: In the opening scenes, when Danny is being chased by the police, his driving position changes from right-hand drive to left-hand drive, then back again between shots.
When Danny Meehan is talking to the Governor in the showers at half-time, the scar on his right cheek is missing.
Monk is described as having killed over 20 people, which would make him one of the UK's most prolific serial killers. At the start of the movie, Longmarsh prison is described as a Category B prison. Monk would almost certainly be deemed a high risk Category A restricted status prisoner, and would be imprisoned somewhere like HMP Belmarsh.
During the explosion in the final scene, the wall can be seen to flex, indicating that it is made of something more flimsy than a real prison wall.