(at around 50 mins) When Justin receives the text and photo of Nikki from Mike upon returning to the club, he replies; however the To: field reads "Nikki".
(at around 43 mins) When the three male leads are "apprehended" inside Nikki's trailer looking for their friend Mike, Kendra smacks Conner across the face with the gun she is holding. In the ensuing scenes blood is seen seeping from Conners nose, scene changes, then it is gone, scene changes again and the blood has reappeared again.
When the group pick up the groom-to-be at the beginning, his golf bag has a long, loose strap that his friend puts over his shoulder. The camera then cuts to him from a different angle and not only is he holding the bag by a short handle but the entire long strap has disappeared.
The "mask" of Mike's severed face has no eyebrows.
After finding Anka unconscious in the bathroom Victor rips Travis's right sleeve off of his shirt right before falling unconscious. Travis' sleeve then appears between ripped and a whole sleeve between shots. The sleeve that Victor ripped off disappeared and reappeared a few times.
(Around 49 minutes) When Travis puts his hand on Nikki's neck, she closes her mouth a bit, despite the fact that she is supposed to be dead.
(at around 1h 20 mins) When Carter escapes in his getaway car just seconds before the building explodes, you can see him accelerate aggressively with the sound of squealing tires, although the car is driving off on a dirt road.
(at around 11 mins) When the group is shown inside the casino during the opening scenes, we see external shots of Las Vegas, but inside shots were clearly filmed at the Greektown Casino in Detroit, as evident by the multiple video screens mounted on the walls displaying the Greektown Casino logo and "Detroit" underneath the logo.
(at around 1h 3 mins) Projectiles from a crossbow are called bolts, not arrows.