Plot hole: When Bruiser (the man who's supposed to beat up Danny) is faking the noises of punching Danny, the two thugs can hear him through the door. But earlier, he punched Danny by accident, then started to talk to him. The thugs should have been able to hear their talking through the door as well. (01:15:30)
Factual error: In the scene when Clooney and Damon are rappelling down the shaft on steel cables, the come up short of the floor. They pull knives and swipe the cables. No knife would be able to cut a steel cable with one swipe.