Continuity mistake: Throughout the movie they are told to suck on the buttons from their shirts. In one scene, once Holloway climbs into the next room, Quentin is sucking on his button. He immediately speaks to Worth, muddling some words because of the button in his mouth. All of a sudden, the button disappears from his mouth and is in his hand again, and he then puts it back into his mouth.
Continuity mistake: When Holloway is hanging outside the Cube from the rope of clothes, it would seem that it disappears at the moment she falls. We see her climbing up toward Quentin, and the rope is around her waist. Then they're holding hands face-to-face, and in the next shot when she slips, the rope stays still. Then, as Quentin goes back inside, it's disappeared entirely, and he doesn't take it back in with him. (00:47:00)