What the hell is so funny about zombies? They have terrible table manners, ripping out flesh and gizzards and stuff with their teeth. And they never floss. They never wash their clothes, despite being constantly covered with blood and whatever that nasty liquid is that keeps draining from their mouths. Plus, they're dead and won't lie down.

And yet, here comes "Zombieland," the fourth leg in an unofficial quartet of undead comedies that began with "Return of the Living Dead" and moved on to "Shaun of the Dead" and "Fido" before arriving here. "Return" is the scariest; "Shaun" is the wittiest; "Fido" is the most sharply satirical. And "Zombieland" is the funniest.

There are several approaches to the horror/comedy hybrid. Some are just so jet-black-humored, you could be forgiven for not realizing their comic content at all. (See "Psycho" and the original "Texas Chain Saw Massacre.") Some try to be near-equally scary and funny. Some derive most of their humor from the you've-got-to-be-kidding-me quantity of their grossness. (Check out "Re-Animator" or "Bride of Chucky.") "Zombieland" is different in that it goes for the mega-grossout while still delivering amusing dialogue and characterizations.

The picture opens with the assumption that America is a sick country. Mad cow disease became mad human disease, which finally morphed into mad zombie disease. Little time is spent in explaining the origin of this plague of the zombies. Just accept that the creatures exist and if one bites you without eating you, you turn into one. If it does eat you, you turn into, well, guess.

Columbus (Jesse Eisenberg, "Adventureland") —” survivors don't exchange real names for fear that they'll become too attached to one another —” is on the road from his dorm in Austin, Texas, to Columbus, Ohio, to check up on his family when he meets Tallahassee (Woody Harrelson, "No Country for Old Men," in full "Natural Born Killers" wacko mode), a tough, cynical loner who loves eating Twinkies and killing zombies.

Traveling together, they meet two sisters: Wichita, in her early 20s (Emma Stone, "Ghosts of Girlfriends Past") and 12-year-old Little Rock (Abigail Breslin, "My Sister's Keeper"). After a rocky start, the four team up and head out for Los Angeles so Little Rock can visit the Pacific Playland amusement park. "You've just survived the zombie apocalypse. Where are you going?" "I'm goin' to Pacific Playland!"

In Hollywood, Tallahassee decides they should hang out in style. Picking up a map to the stars' homes, they drive to the palatial estate of his favorite actor, and we go crazy with what is the funniest movie cameo I've ever seen. By now, you probably know who it is, but just in case, I'll keep the secret. The Mystery Guest is perfect and the behind-the-scenes laugh is that he wasn't the first choice. Sylvester Stallone and Matthew McConaughey, among several others, turned down the chance. There is no joy in their huts tonight.

This picture does for zombie movies what "Ghostbusters" did for the haunted house genre: respects its conventions while twisting them all out of shape. The emphasis is on comedy, rather than on horror with comic touches.

First-time feature director Ruben Fleischer has tossed in a couple of very effective pop-ups, but co-writers Rhett Reese and Paul Wernick (TV's "The Joe Schmo Show") stick pretty close to the funny bone. Look for Reese in a cameo during the opening credit sequence. While his name is on the screen, he's up front firing an AK-47. Wernick was asked to be a zombie in that shot, but didn't want to mess with the makeup.

The four leads all get their laughs, but Harrelson is the guy you'll remember. He seems to be having a ball sending up tough-guy adventure movie heroes. There hasn't been a slyly tongue-in-cheek performance like this since Kurt Russell and John Carpenter had that "Big Trouble in Little China." When Tallahassee meets his movie idol, the Mystery Guest, the over-the-top childishness of his pleasure almost causes Stone to lose her composure.

The film's plot isn't flawless, and it contains some elements that are more handy than rational. Why, for instance, is electricity still flowing freely everywhere? Stashes of guns and ammo are discovered just when needed most, although that point may be a deliberate joke. Harrelson gets one of the movie's biggest laughs when he finds a bunch of automatic weapons in a duffel bag and yells, "Thank God for rednecks!"

Hard as it is to believe about a zombie movie, this is the funniest film of the year. It has what most zombie movies lack and badly need: brains. —”Doug Bentin