When Detective Loki is speeding to the hospital at the end, he passes the same restaurant (with a red awning) three times: once as he pulls off the smaller road onto the major road, and twice after that.
The sink in the abandoned building's bathroom where Alex is being kept goes back and forth between shattered and intact throughout the film (after being shattered, of course).
After the RV rams the tree and is later undergoing forensics, the grill is pushed in and the windshield is broken, but surprisingly there is no no other damage to the front of the RV, including the hood.
When Detective Loki goes to question Bob Taylor at his home (the house with the snakes), the mailbox pole by the driveway shows the address number as "4261" but when Loki calls for backup he gives the address as "437 Carrol Street."
When the families gather to celebrate Thanksgiving and they meet, there are two cars in front of the house. But when the girls are already lost, they go out, and there is only one vehicle.
Detective Loki works for a municipal police department in Pennsylvania yet all of the police cars with lights activated have only blue lights. Blue lights in Pennsylvania are "courtesy lights" for volunteer firefighters/EMS personnel private vehicles. They are not emergency lights with any traffic control powers. Police use either a combination of red and blue or, if using a single light, red only.
When Keller is deer hunting with his son, the two families are celebrating Thanksgiving. The film takes place in Pennsylvania, where deer hunting season does not begin until the first Monday after Thanksgiving.
When Loki searches the home of the suspect with the snakes, he breaks padlocks on the suitcases far too easily. You cannot hit a padlock twice with a crowbar and manage to break it.
When Alex is untied by Nancy, he hasn't eaten or had water for four days, while being tortured. It is unlikely he would have had the energy to break the bathroom glass in an attempt to escape, as he would have been exhausted. However, clearly Alex would have had both food and water as Keller wants to keep him alive.
The film is set in Pennsylvania, which, as shown, does not require front license plates.
The movie is set in Pennsylvania yet there is a billboard advertising Atlanta law firm Morgan & Morgan above the liquor store (which, in PA, would be state-run, not privately owned).
When Detective Loki reads the newspaper in the hospital, the article titled "Car crash sends two to hospital" has only three paragraphs that are multiplied.
When Detective Loki is on the computer looking at the obituaries a little over halfway through the movie, the taskbar of the computer can be seen, and it shows the symbol for no network connection (a computer with a red 'X' over it) even though he is obviously supposed to be online.
When the river is being searched at 32:56, a "Conyers Fire Dept" rescue boat is seen. Conyers is a suburb of Atlanta, Georgia, but the movie is set in Pennsylvania.
When Keller Dover is smashing the bathroom sink, you can see that he's using a prop hammer. When he holds his arm up, the handle near the "cheek" of it bends. It then straightens itself out after he puts it into the wall next to Alex Jones' head.
When detective Loki reads William Dover's Obituary in Palocalnews.net, on the computer, the date and time shows 2/27/2013 2:52pm. The movie takes place before Christmas.
Around the 26:57 mark, it appears that Detective Loki has a toothpick in his mouth while Keller approaches him at his car. However, in another scene, he doesn't have the toothpick.
Early on in the film, in the neighborhood Steller's jays are calling. These birds are not found in Pennsylvania. Their range only extends from the Pacific Coast to the Rockies.
The area code on Dover's truck is 570, which is the Scranton/Wilkes Barre area of Pennsylvania, but the license plate on Loki's car indicate Montgomery County, which is a couple of hours south and does not use the 570 area code.
Loki finds a victim he believes has been injected with a drug. He looks at the vial briefly before throwing it on the ground and taking the victim away for treatment. Nobody with his training would have thrown the vial away; the label would identify the drug and strength, and give a clue as to the amount used, all helpful for successful treatment.