Revealing mistake: In the very beginning when we are flying over the dead town in a helicopter, look closely at one of the very first shots of the "empty" city. On one of the left side streets you can see a car driving down the road. It's not a character mistake because she is looking hard out the window and should have spotted the moving car.
Revealing mistake: Just after Rickles has his face torn off, you can see that there are no veins on the side of his eyeballs.
Revealing mistake: In the very beginning of the movie, Laurie Cardille is sitting looking at a wall with nothing but a calender on it. She rises and walks up to the wall to get a closer look at the calender. Suddenly hands come out of the wall. If you look closely, you can see the round marks on the "cement" block wall where the hands will come out. Viewed best when freeze framed (which is permitted for a revealing shot such as this one), just before hands emerge.