When Barbara is loading the Henry lever action rifle, she is loading the cartridges bullet first. This would lead to a malfunction in the rifle, as the bullet end must be facing toward the muzzle for the cartridges to properly feed from the magazine tube into the chamber.
(at around 1h 18 mins) At the end, when the two country guys are at the cellar door, one is using a chainsaw to cut through the door. The film shows him cutting through the 2x4 on the inside of the door even though the hole in door shows he should have clearly cut through it already.
In one scene, it shows 3 zombies abreast moving toward the camera. Two of them are moving in the typical zombie manner - slowly and mechanically. The third zombie (on the right) is moving much faster than the others. The scene cuts briefly to another scene then it cuts back to the 3 zombies. The one on the right is now moving much slower like the others. When the camera first cut from that scene, the director undoubtedly chastised the third actor zombie and told him to slow down before doing another take.
Barbara is seen on several occasions firing many shots from her rifle while gripping the barrel with her left hand. In reality, after just a few shots the barrel would become far too hot to handle in this manner.
(at around 58 mins) In the scene preceding the venture to the gas pump, Ben creates a makeshift torch out of a table leg. He continues to shake a can of lighter fluid over the rag, implying that he is dousing the rag in fluid, but when he does so, the spout of the can is not open. No fluid would be able to pass through.
Both in scenes where Barbara is loading the rifle, and where she's wearing the policeman's gun belt across her chest, anytime the head stamp of the bullet is shown you can see that the primer pocket is empty, meaning the rounds are dummies.