When Ella Purnell first met Tim Burton to discuss her role in "Miss Peregrine's Home for Peculiar Children," she saw a man with "cool" hair dressed in jeans and a t-shirt. "He doesn't look how I thought he'd look," she recalled, joking, "I guess, in your head, you're like, 'He's gonna be riding a unicycle with a handkerchief in his pocket.'"

On set, her co-star Asa Butterfield said his first impression was of a very "collaborative" director: "He wants you to have your own ideas and share your ideas, and he'll do the same."

It was a brave new world for these two young actors, who were working for the first time with the man behind "Beetlejuice," "Edward Scissorhands," and "Corpse Bride." What they discovered on set were some of the strangest things they'd ever seen. During interviews for the film, Purnell and Butterfield walked us through some of the most memorable visual effects of Burton's latest.

The Carrot"The carrot scene, the carrot was real," Purnell said. "Obviously, the growing was CGI-ed, but when she tried to pull it out, Bronwyn -- little Pixie [Davies], who is so good, by the way -- that was actually a stunt guy dressed in green on the floor pulling the carrot on the other side ... It was one of the strangest things I'd ever seen, only on a Burton set."

The Stop-Motion ToysTim Burton on the set of "Miss Peregrine's Home for Peculiar Children"One of Asa's favorite effects came during an attic scene with Olive (Lauren McCrostie) and Enoch (Finlay MacMillan), who brought a couple of creepy dolls to life for a battle. It was stop motion layered over live action. "That was really exciting," he said. "I didn't actually get to see them because they really did it afterwards and then put it on but the dolls themselves were all sort of weird and creepy."

The Pub Fire"There's this one scene where we're bursting out of a pub," Butterfield explains. "We first escape and [Olive] sets the pub on fire and puts her hand on it, and they wanted real fire so they had this whole rig set up around the rim of the door and windows where they would pretty quickly have these roaring flames, and we'd run out and the flames are coming behind us." The crew enlisted stunt men, as well, who wore fire-proof suits so they "could actually be on fire" and roll around on the ground. "So that was pretty exciting," he said, "and every time we did it they had to pain the walls of the pub because they got scorched."

The FloatingDF-07504 - Jake (Asa Butterfield) makes sure Emma (Ella Purnell) stays relatively down to earth. Photo Credit: Jay Maidment.To portray Emma, a peculiar with an affinity for air, Purnell had to work for about 10 days with a movement couch. Wires did most of the heavy lifting, but she still had to appear as though she were lighter than air. "We had this great technique where you had to push your hands [together] really hard and then you let go and they float up," Purnell recalled, "and it's actually just letting the air take you and feeling lighter than air, and envisioning what a balloon would look like. I spent so long blowing up balloons and letting them float around."

Underwater SwimOne of the main visual pieces was already spotted in the trailer: Emma takes Jake down to a sunken ship in the ocean where she uses her abilities to fill the vessel with air. "It's about six days of filming for literally two to three minutes of screen time," Purnell says. "I mean, do the math. I mean, that's mental: 30 seconds per day. My mind is blown."

She and Butterfield filmed the scene in a massive tank in Pinewood Studios. "We were in a pool, we were underwater, but the entire time it was painted green, so you do kind of feel spaced out because you have no sense of depth," he said. "Everything's really blurry anyway because you're trying to open your eyes underwater and I wear glasses so that didn't help."

"I also couldn't swim before doing this movie," Purnell recalled. "So I learned how to swim. Well, I could swim, I could do the doggie paddling, but now I have to do the breast stroke ... Yeah, it was really tough. I was really terrified, but I tried to keep it together."

At the time, she had just finished her final exams of high school as an 18-year-old, a moment she says felt freeing. "Sometimes you just have to be like, 'Screw it. I'm just gonna live this experience and do it,' and I guess this year has been -- and last year has been, since I finished school -- all about new experiences. And there's something sort of vaguely terrifying about being weighted and being pulled down to the bottom of a tank, with weighted shoes on and a wig and a silk dress, and you have a breathing mask and then they take it away and the surface is so far up and there's a second where your body is screaming and it's like, 'Get me to the surface!' and then you just let it go and it's amazing. It's amazing, your body just feels free, it's therapeutic, it's kind of beautiful."

"Miss Peregrine's Home for Peculiar Children" opens in theaters Friday, September 30th.