Columbus: You see? You just can't trust anyone. The first girl I let into my life and she tries to eat me.
Woody Harrelson locks himself in the booth at Pacific Playland and locks/closes the security screens on three sides. After he is surrounded by zombies, one of the side cages has been pushed opened a bit, leaving quite a gap. The scene pans around to various angles as Woody fires away, and in a subsequent shot, the screen is shut again. With both his hands full, he couldn't have shut it.
The guy at the gas station is also the guy that gets eaten by a zombie whilst on the toliet at the start of the film.