Zombies are big again this year.

And if you visit "Terror Behind the Walls" - the annual scarefest at Eastern State Penitentiary - you'll see the brain-eaters lurching throughout the grounds: zombie prison guards, zombie prisoners, zombie patients in the infirmary.

"You're so gross! I love it!" makeup artist Nickki DuBan gushed to a zombie wannabe whose lips dripped dark blood. (Actually, a mixture of food coloring and chocolate syrup.)

DuBan paused, then added, "It takes a certain kind of person to work here."

The folks who do are so good that, last year, AOL City Guide named "Terror Behind the Walls," going on now until Nov. 7, the No. 1 Haunted House in America. Last month, Haunted Attraction magazine, a go-to guide for the scare industry, did a cover story on "Terror" with the subheading, "You go to jail. . . . You go to Hell."

"If you want to learn about Eastern State, come during the day. If you want to be entertained, come at night," Eastern State program director Sean Kelley said.

This year's theme is "Infirmary." It takes visitors through a prison medical wing that includes empty waiting rooms, sterilization chambers, and a morgue. 3D glasses enhance the experience at certain points.

In haunted industry terms, "Terror" is "high startle, low gore," Kelley said.

It is also high profit: More than half of the historic site's operating budget comes from the proceeds. Last year's frightfest brought in 65 percent of the budget.

"It's crucial to what we do," Kelley said.

Visitors don't see what goes into transforming normal-looking, living people into the restless, evil undead every night. Using things as mundane as oatmeal and air conditioner filters, a team of 12 makeup artists paints and preps more than 120 actors in less than three hours.

But almost anyone can re-create the looks. Here's how:

Zombie-licious

1. Mix equal parts gelatin and hot water, and stir. (If you are buying gelatin packs, one or two should be enough for one face.) Add a few teaspoons of oatmeal for texture.

2. Using a popsicle stick or spoon, apply the cooled mixture in blotches to a clean face. You're trying to achieve the effect of skin rotting away in certain places.

3. Let set. Dab latex or eyelash adhesive over oatmeal and gelatin mixture. Use a cool hair dryer to speed setting. Option: Dab on castor sealer to help the makeup blend better.

4. Dab pale blue or white makeup - eye shadow works well - over face with a stipple sponge, then blend with a makeup wedge. You can make a stipple sponge out of air conditioner filters available at any home improvement store.

5. Fill in eye sockets; "Terror" makeup director Kristen Phillips likes red or purple here because it looks "more diseased," but some people prefer black. Use darker-colored makeup to accent hollows or low areas of face, like cheekbones or pulse points, under nose and chin.

6. Dab purple on oatmeal "zombie rot." Highlight with base color and red.