Why would supposedly savvy Columbus let other people get the drop on him twice? He knows all about zombies, not people.
In Columbus' flashback, he is shown playing World of Warcraft. Close examination shows that he played as a Night Elf, a race belonging to the Alliance. Apparently Columbus has been battling the Undead long before they came to his doorstep.
Columbus didn't have Rule 31 (Check the Backseat) until after the incident in Garland. Because Rule 32 is something he picks up not long after with Tallahassee.
The climax is a send-up of zombie games - there's Tallahassee on the rail shooter sections on the roller coaster and the tilt-a-whirl, Columbus in the claustrophobic survival horror section in the haunted house, and the girls on the high ride with the co-op Hold the Line-style game.
The Reveal about Tallahassee's son is worse than initially apparent. Consider how unlikely a clean or quick death would be. And consider who would have to put the resulting zombie down.
Columbus states that when the Zombie Apocalypse began, the first people to die were those who were fat and obese. Why exactly? Because they didnt have the energy to run away, thats why. Plus, all the flesh on them possibly made them a mouth watering target for the cannibalistic Zombies. Columbus makes a point of this when explaining the importance of his first rule, Cardio.
One of the opening clips showed an older woman fleeing from a party full of infected little girls. While she could have easily been a neighbor of the partygoers, given her shirt and all the stuffed animals in her car, what if she was one of the girls mothers??? Imagine the horror of having to run from your own child who's been turned into a monster.