The killer string a piano wire across a doorway at the correct height to cut the throat of a victim attempting to flee. This is wrong for two reasons: 1) The killers had no idea who would flee using this meaning that the wire could have caught a taller fleeing in the chest, not the throat and 2) The person (in this case,a woman) wasn't running fast enough for the wire to slice deeply into her throat. At best, it would "clotheslined" her and thrown her to the ground or seriously injured her windpipe.
MAJOR PLOT HOLE (SPOILER)
Since the killers outside can see everything inside because the lights are ON, it would have seemed that someone (including the surprise survival expert) would have immediately suggested turning the lights OFF. However, at no point during the film does anyone ever suggest taking this blatantly obvious safety precaution.
Minor Plot Hole
Although everyone is shown having a cell phone and the cell phone signals are blocked, no one shown ever checking their phone before sitting down to dinner or turning the phones off. Had this done either of these very routine actions they would have noticed that the signal was being blocked.
Minor Plot Hole (Spoiler)
Erin, the heroine of the film tells everyone multiple times to stay away from the windows. Yet she routinely looks out the windows throughout the film and is attacked twice while doing just this.
Minor Plot Hole
A character is struck in the upper thoracic cavity with a crossbow bolt, in what appears to be his right lung. This is an incapacitating wound that would fill the lung with blood and that would prevent the character from doing anything. Yet he continues move about for at least 25 minutes of film time after this occurs.