When Mary is at the river, she washes her skirt and we can see how it is soaked in the water. After she shoots the man that is chasing her, Shannon comes to her and when they both are running back to the house it's completely dry.
Struggling to stay alive in a dangerous post-apocalyptic world, Mary still keeps her armpits and bikini line clean shaven.
On hearing a distant shot in the dark, the gang leader immediately cries out, somehow knowing his son has just been killed, and yet he didn't even know he was missing.
On four occasions when her life was threatened, Mary is seen pumping the action of her shotgun near the end of each incident, not the beginning, meaning that for much of the time that she was relying on her shotgun for defense, it was unloaded and unable to fire, i.e. useless.
During the main attack Adam encounters two gang members trapped in the basement and cocks his rifle to shoot them, and later when he returns to help Mary he cocks it again, meaning that for much of the battle it wasn't loaded and ready to fire.
Shannon and Adam easily escape out the back door of the burning house, implying that the cannibal gang that set the initial trap were too stupid to realize that might happen.
The closed captioning for this movie lags about 15 seconds behind the audio. For those relying on CC, it makes this movie almost unwatchable.