Continuity mistake: At the TV station, when Fran takes control of the camera, notice a man with a sweater and a beard behind her, but in the very next scene the same man appears with a different shirt on. (00:04:40)
Continuity mistake: In the beginning of the movie at the TV studio, Steven tells Fran that they are meeting at 9:00 to take a helicopter out of town. When they take off in the helicopter and fly away, there is a giant digital clock on a building in the background that reads 6:00. (00:05:05 - 00:18:50)
Revealing mistake: When Stephen first approaches Fran, who's manning a television camera, he says "meet me on the roof at 9 o'clock. We're getting out in the chopper." She replies "What? David we can't", referring to the character, Steven, by the actor's real name (David Emge). (00:05:10)
Continuity mistake: Early in the movie, Peter enters the basement and has to exterminate zombies in a cage. He fires seven bullets from a six-chambered revolver without reloading. (00:15:05)
Continuity mistake: When the old car blows up both of the dead zombies are gone. (00:21:40)
Continuity mistake: When they stop to refuel the helicopter at the abandoned gas station, a zombie approaches from under an airplane. In one shot, it is holding onto the wing support next to it - in the next shot, the zombie is standing in front of the support with its hand at its side. (00:22:25)
Revealing mistake: When Peter shoots the door the first round goes through, but the second shot just shows a flash of light behind the piece of paper on the door and never goes through. (00:22:40)
Factual error: When they are refuelling the helicopter (as a zombie approaches quietly from behind) the actor has put the gas nozzle not into the hole for the gas tank, but into one of the foot-holes that helicopter mechanics use to climb up to the top of the helicopter to do repairs. It doesn't even fit properly. (00:22:55)
Visible crew/equipment: In the rural airport scene a zombie is killed as Roger is filling the helicopter with fuel. As the zombie falls off the boxes, the tubing that pumped the blood is coming out of his pantleg. (From the Divimax widescreen DVD) (00:24:00)
Other mistake: At the small airport after the heroes flee Philly, Peter walks into the office and is startled by a sound beyond the door. Thinking it is a zombie, he begins to fill the door with holes, about five of them. On the last shot, the door merely chips and does not leave a bullet hole. This can only be seen in the DVD version. (00:25:00)
Continuity mistake: The zombie that attacks the helicopter at the gas station loses the top of its head to the spinning rotor, causing gouts of blood to flow down its front. In the shot as it falls over, the blood has miraculously stopped flowing and is now a dry stain. (00:25:20)
Visible crew/equipment: When the two kids in the airport attack Peter and try to bite him, notice in the top right corner a crewmember's hand comes into shot. (00:25:40)
Continuity mistake: Peter and Roger are attempting to hold off some approaching zombies while trying to get the door to Penny's shut. Peter then throws his gun and the keys into the store. In the very next shot he is trying to pull the same keys out of the lock on the door. (00:37:35)
Visible crew/equipment: When Peter is attacked coming out of a doorway (after he leaves the boiler room) he wrestles with two zombies. If you pay attention to the bottom of the screen, just before he pushes the zombies away, you can see the hands of a crew member come into the frame. They were probably making sure none of the zombie actors fell into the camera. 2003 Directors cut DVD version. (00:49:02)
Visible crew/equipment: In the scene where Roger and Peter are getting the trucks to block the mall entrances, in one shot when they are both in the same truck you can see, in the side window, a crew member is driving a white van. After Roger gets out of the truck the van is gone. (00:55:00)
Revealing mistake: After Peter and Roger pull away in semi-trucks, traffic can be seen behind them on the road. (00:59:16)
Continuity mistake: After parking the first truck in front of the mall doors, Roger jumps out and runs towards Peter's truck. Notice the zombie wearing the red and black striped rugby shirt. After Roger runs past him, he breaks zombie character and becomes concerned about his shirt being tucked in. (01:00:50)
Other mistake: In the aerial shots of the semis being driven in the mall parking lot, the zombies are milling about. Notice they have left a path just clear enough for the truck. (01:02:40)
Visible crew/equipment: When Roger hits the zombie with the truck, notice at the bottom right a trampoline from which the zombie jumps off. (01:04:55)
Continuity mistake: When a zombie's head is held up in the truck to be shot, there is a big splatter of blood down on the face of the soldier. He wipes a very small amount of blood off, but when he gets into the other truck he is perfectly clean. (01:05:05)
Answer: One of the cops that was with Joe Plato (how much you have seen of them will depend on which version of the movie you, but I HIGHLY recommend the fan made/edited 'Extended Mall Hours' cut on YouTube) asked them for cigarettes. You'll notice that Roger and Fran lit up cigarettes as they were taking off, that's what Roger was laughing at.