There are genuine, body-tensing moments of terror and amazement in "Harry Potter and the Cursed Child" that might cause one to wonder, perhaps aloud to a seatmate, whether an ambulance is on standby outside the theater if, say, there's a mishap with one of the flame-throwing wands.
Heat from the flames can be felt on faces in the crowd.
Without giving away too much, there's also a man-eating book shelf, pulses that somehow rock the theater in moments of time travel and a potion that mutates one character into an entirely different human.
Jamie Harrison, the illusionist and magician who created the magic on stage, tallies these audience reactions — wide-eyed whispers and wows — with the zeal of a big game fisherman whose line's gone taut.
"When you've created a moment that captures people's imagination and surprises them in a way they weren't expecting, I think that is just one of the most fulfilling moments," said Harrison, 46, who is based in Glasgow, Scotland.
"I love reading about the history of theater and spectacular events. Some of the things we used to do, particularly in the Victorian and Renaissance periods, were simply incredible and I am not sure that actually what we're doing in the modern theater is as spectacular as what they used to back then if I'm really honest," he said.
He cites moments in theater history where riders would jump from horse to horse as they galloped atop a rig akin to a treadmill, galleon ships swaying on a special stage flooded with water, and a stage floor opening up to reveal a cave that's been dug into the actual soil under the theater.
"There's a lot of things that have been done in the past that were pretty spectacular and I like to feel what we're doing at the moment is on that continuum, I feel part of the continuum," he said.
"I think people quite often think, 'Where do you get your tricks?' But 99% of the magic in the show is original and a lot of that is from a backlog in my head from being obsessed with magic since I was a child."
For Harrison, the magic seed was planted when, as a boy, he began fiddling with a rigged deck of cards and a coin trick during a stint in a plaster cast after accidentally dislocating his knee after a collision with his grandparents' wooden floor.
"It just gave me a whole new thing in my life, and I remember asking my uncle if he wanted to see a trick and he was like 'Yeah. Cool.' But I could tell that he was thinking 'Oh this is going to be rubbish' and the trick blew his socks off and I had a real moment of 'Oh, my goodness. I just amazed my Uncle John' and I just got the bug and spent every penny on buying new books and tricks and going to magic conventions."
Harrison was driving in rural Scotland nine years ago when he got the call asking if he'd take on the "Harry Potter" production.
"I hung up and got out of the car and sort of ran up and down the side of the road next to these fields of sheep with excitement," he said.
It debuted eight years ago to the extreme delight of audiences in London.
"At the time there was a lot of questioning in the press if 'Harry Potter' could work on stage, whether the magic could ever deliver compared to the films, and you start to question that yourself," Harrison said.
Ideas originally took shape with gaffer tape and string and became polished after much trial and error with the help of numerous professionals, including architects, engineers and electricians.
"There are so many computers and automation systems and specialist desks for all of the different things that need to happen in the show that you just wouldn't believe it. It looks like NASA if you go and stand at the back. There are, I don't know how many, I've never counted, but so many screens running the show," he said.
But there's old-fashioned magic, too.
For instance, a lot of sleight-of-hand practice went into carrying out the Expelliarmus spell in which a wizard is disarmed of a wand that flies into the hand of spellcaster.
"The trick was so hard to achieve, there were moments when we were tearing our hair out thinking, 'Do we just cut this from the show?' But it kept evolving with tiny changes over and over to the point where we were literally shaving millimeters off various different metal components for a period of months, and then one day it all just clicked and it suddenly worked and we all went out for drinks," he said.
It was the trick that "Harry Potter" author JK Rowling wanted to see again when she first saw the show.
"That was one of the most nerve-racking experiences of my career, but it went brilliantly," Harrison said.
Untold care went into using illusion and magic in a way that didn't interrupt the flow the play, but instead added to the emotional journey of the story.
"I genuinely think that the version that people are seeing in Chicago is the best version of the show," said Harrison, noting the perpetual stew of tweaks and changes the show — originally shown in separate three hour installments on consecutive nights — underwent to get to this point.
Harrison spent a week in Chicago before the show opened in September to make sure everything was up to snuff. He had dinner along the riverfront and went on an architectural boat tour. He planned to spend more time here but had to get home to celebrate the adoption of his second son.
"Being a parent absolutely changed the way I experienced the show through that filter," he said.
Between all the magic and adventure, the play is about a father and son coming to understand themselves and each other.
"It's amazing how intoxicating theater can be when it's at the standard that everybody's work is on 'Harry Potter,' " said Harrison, whose credits also include the stage prequel to the hit Netflix series "Stranger Things."
As far as pulling back the veil a millimeter or two on how it is he accomplishes the magic and illusions seen in the show, Harrison responded: "You've got a 100% zero chance of getting me to tell you how anything is done. ... It's really important to maintain the audience's experience."
Had to ask.
