#5. They Can't Handle the Cold
Zombies are dead meat. No arguing that; it's their one defining characteristic. But everybody focuses on that "dead" part like it's such a huge deal. They often forget about the "meat." Do you know what else is dead meat? Steak, hamburger, possibly even that red grease mush inside of Taco Bell food.
Look at it.
When flesh is alive, it's got all sorts of defense systems to keep it that way. When it's dead, you have to throw it away in about a week even if you seal it up in plastic and keep it at a carefully modulated temperature. Now, your first inclination may be to think of cold as dead meat's friend, after all, the surest way to defeat that week-long deadline is to freeze steak, keeping it fresh for months. But don't forget: Unregulated cold does awful shit to formerly living things. If you live far enough north, the zombie apocalypse will probably work itself out the first time it tries to go outside. The first zombie-killer is the simple fact that the human body is mostly water, and water freezes. Once the temperature drops to freezing (or near it with a high wind chill), zombies will become significantly more rigid.
No word on them transforming into snow monsters.
After enough exposure, a dead body is going to be frozen solid and not chasing down any screaming victims, no matter how delicious and Rascal Scooter-bound they might be. It's also safe to assume that zombies wandering around in a wintry wonderland are not going to be wrapped air-tight in plastic like we do with food, so freezer burn becomes an issue. Seriously. The same thing that ruins your ice cream also ruins the Undead Onslaught. The freezing of the flesh at night, combined with partial thaw during warmer days, then refreezing again sets up the perfect conditions for the onset of freezer burn, which results in the cells dehydrating as water evaporates, even when frozen solid. Freezer burned meat isn't just dead, it's destroyed.