Continuity mistake: Thomas takes the blade of Theresa at the top of the tower. When he does, his grip on the blade changes position and the hand changes too. (00:55:30)
Continuity mistake: After Minho and Thomas escape from the blades of Section 7, they are crawling through a small passage with the ceiling coming down on them slowly. In one shot, the ceiling is touching Thomas' back. But in the next shot as they get out, he still has a few inches of clearance.
Continuity mistake: When the Griever "drools" on Thomas for the first time, it leaves a big visible trail of drool/slime. Camera cuts and the big visible trail has disappeared instantly. (00:37:00)
Continuity mistake: Ben gets hit round the head with a stick and blood appears. However when they start to carry him to the pit, the blood disappears in some shots. (00:22:30)
Chosen answer: As it turns out, Gally was being mind-controlled by the people who operated the maze. This would explain why he was highly against any form of escape plan. When the others escaped, the operators gave him some form of safe passage straight to the control room.so he could kill the others. Best guess is, they re-activated the elevator for him and he took that route...but that's left ambiguous.
Gavin Jackson