Revealing mistake: When Loomis shoots the marshal's window out, when he makes a u-turn you can see the tire marks on the road and dirt from previous takes.
Revealing mistake: At the end when Snake drives over the hidden land mine and the cab is blown in half you can see three sets of wheels under the front half of the cab and a strange looking flap probably used to conceal them. (01:24:50)
Revealing mistake: When the mounties are attacking Johnson's cabin, one of the men with them crawls into a bear trap. You can plainly see that the jaws of the trap are made of rubber or some other soft material when he struggles.
Revealing mistake: Burke kills Mary Roberts. She blinks when he turns her head to check out her face. (00:47:10)
Revealing mistake: When Da Silva has finished shooting on the police firing range, the camera does one last shot of the target and you can see the squib detonator wire hanging from the hole that's just been created in the head area of the target.
Revealing mistake: When the photographer is shot by Thana, his blood can be seen being thrown from offscreen. (00:36:54)