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)
Answer: Thomas was placed there by the lab workers at W.I.C.K.E.D. Boys were being sent up once a month in it as part of an experiment. Thomas, however, works for W.I.C.K.E.D. Although his memory was wiped like the other boys, he, and also the girl, knowingly took part in the experiment in order to change the conditions of the test.
raywest ★