BROWNSVILLE — Lions roar. Tigers growl. And starting today, thousands of people will be going to Boo at the Zoo.

The Gladys Porter Zoo’s 28th annual Halloween celebration today and tomorrow likely will draw thousands of people from all across the Rio Grande Valley to Brownsville.

“I want to say it’s the biggest Halloween event in the Valley,” zoo Public Relations Coordinator Charlie Abrego said, adding that 14,000 people attended the two-day spook-fest in 2016.

By all appearances it was business as usual at the zoo Thursday afternoon. But behind the scenes, volunteers and staff were working overdrive to prepare props for all the tables that will be set up with candy and games for kids.

Groundskeepers were stringing lights throughout the grounds. And after hours, volunteers from Pace Early College High School’s Skills USA club were busy putting the final touches on the haunted house.

“They’re teenagers, so, they are all about it,” Abrego said as a prop skeleton sat on a scissor lift in a staging area, waiting to find a home somewhere in the haunted maze of creepy dolls and blood-spattered walls; all red paint, of course.

“The kids are pretty creative. You give them a little theme and they take off.”

But don’t worry if little ones want to take a tour of the popular haunted attraction.

“Even the little kids, when they’re here and want to come in because they are just so interested, so what we do is we do a guided tour when you have little kids,” he said. “You just let us know and somebody will walk with them, one of the volunteers, so that way the actors know not to be too scary.”

Once they exist the haunted house, Boo at the Zoo-goers can wind their way through tables filled with candy and games — Abrego said the zoo spends about $10,000 on candy, so be prepared — to the Russell Aquatic Ecology Center.

There’s an extra cost to enter, $2.50, or 10 tickets, which can be purchased at the door or online, but it’s well worth it, Abrego said.

“They’re going to have Gulf Coast mermaids swimming in the tank. The kids love it,” he said, as two mermaids provided a demonstration in the 32,000 Gulf Coast tank where sheepshead, drum and other local fish encircled them. “It’s not so scary like the haunted house. It’s a big hit.”

The best part of Boo at the Zoo, and one of the reasons it is so popular, is it’s a cheap and family fun way to spend Halloween, Abrego explained.

“There’s nothing compared to other events in the Valley or in Texas,” Abrego said, while winding his way through the zoo’s popular haunted house exhibit. “It’s a low-cost event that the whole family can enjoy.”

Pre-sale tickets were $2.50 while the day-of cost is just a dollar more. Tickets can be purchased online at the zoo’s website and at the zoo entrance.

Of course, none of this would be possible without an army of volunteers, about 600 to 700, and the zoo’s sponsors, Abrego said.

“It is the most challenging event we have because so many people are involved with the zoo to organize it. But everybody really enjoys it and once the event is happening, everyone is real excited and you see other people in costumes and it provides family time,” he said. “It’s a safe alternative to trick or treating out in a neighborhood. It’s a controlled environment.”

And it’s a spooky one, too.

IF YOU GO

WHEN: 6-9 p.m., Today, Tuesday

WHERE: Gladys Porter Zoo, 500 E. Ringgold St., Brownsville

COST: $3.50 per person. Free for zoo membership holders