Character mistake: G. Peppard holds up a Walther P-38 pistol and calls it a Walther PPK.
Continuity mistake: When Gatou Vardebedian is holding Gus Cardinale at gunpoint, the gun keeps changing position between shots (under his throat, by his nose...) and she is holding it straight or turned sideways. (00:13:00)
Revealing mistake: At the start of the film, where West and Cain are re-animating dead soldiers, one of them tries to kill West. So, he shoots him in the head. It's obvious that West's gun doesn't fire, and the soldier just pretends like he's been shot.
Continuity mistake: Kari and Traci are both wearing sandals barefooted when they are caught toilet papering the house by Tom and Finn but when the four of them go for a walk on the beach minutes later, Kari is now wearing grey sneakers and Traci has black socks with her sandals.
Continuity mistake: When the zombie Barry falls on Jordan, he's played by an obvious stunt double who isn't wearing any zombie make-up.
Plot hole: Georges repeatedly tells immigration officers about his Africa trips. This overlooks that fact that INS would have or request a copy of his passport to process his case. In real life, INS would have realised immediately that the Africa story was not real: no entry/departure stamps in his passport.