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)
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)
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)
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)
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)
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)
Continuity mistake: When Roger and Peter are blocking the entrances with the trucks, Roger kills a zombie with a long beard that is walking towards him between the trucks. Later on in the movie, we see the same zombie, in the same clothes, outside the doors, trying to get in. (01:07:35 - 01:17:15)
Continuity mistake: In the scene where Roger gets the bag and drop it on the floor whilst trying to get back to the truck, he gets bitten on his left arm. But in the next shot the bite mark is gone and then the bitten sleeve is on the right side. (01:08:05)
Continuity mistake: After the four arm themselves, they go to raid Penney's. As Peter and Roger roll up with the wheelbarrow, Francine shoulders her rifle. There is a cut and she shoulders it again. (01:13:35)
Continuity mistake: When Stephen shoots a zombie clinging onto the car, whilst driving off there manages to be a streak of blood in front of the zombie where the previous take took place. (01:17:10)
Continuity mistake: Immediately after the three men close the first door, when they are driving away Flyboy can be seen in the trunk aiming a handgun. It cuts to his face and he's holding a radio, talking to Fran. (01:18:10)
Continuity mistake: After the doors are closed, all the remaining zombies are exterminated. In several shots we see prone bodies with puddles of blood around the head. Later, when they are cleaning up the bodies, there are no blood pools around any of them. (01:20:00 - 01:23:30)
Continuity mistake: When the raiders enter the mall you see Blades (Tom Savini) enter the mall and run around, although when it shows the bikers outside the mall Blades is sitting on top of the red van. (01:46:30 - 01:47:30)
Continuity mistake: When the bikers are in the mall, a zombie is killed next to a teepee. Another zombie is pushed into the teepee knocking it over. As it falls, you can see the first zombie starting to roll out of the way. (01:47:45)
Continuity mistake: When the bikers are stealing the zombie's wallet notice Blades in the background cheering his buddy on while just standing next to a zombie. (01:48:30)
Continuity mistake: When the sweater vest zombie first goes up to the 2nd floor he appeared coming up to the 2nd floor moments later.
Continuity mistake: Near the end, Steven is in an elevator, and the zombie opens the doors and starts biting him. When he gets them all out of the elevator, blood comes out of his mouth and down the right side of his face. But later the elevator doors open and Steven is a zombie and the blood is on the left side of his face.
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.