The stage adaptation of Mary Poppins is not the kind of show where the actors can afford to let their concentration lapse.
There are several precise and tricky cues for the cast to hit across the three-hour West End production.
Props have to appear from (or disappear into) thin air. There are magic tricks. Characters dance upside down on the ceiling. There are scenes that involve complex choreography, kite flying and statues coming to life.
It's a testament to how tightly rehearsed the show is that nothing went wrong at the show's opening night on Wednesday.
"It does sometimes!" laughs Zizi Strallen, who plays the legendary leading role. "But there are contingency plans, that's the beauty of live theatre, and it's my job to cover it up as well if it does go wrong."
The most complicated part of the show, she says, is a scene which will be familiar to fans of the original 1964 film starring Julie Andrews, where Poppins is seen somehow pulling huge items out of a relatively small handbag.
"Not only am I singing and being Mary Poppins, I'm then essentially doing magic tricks," Strallen explains, crediting the magic specialist who was hired to teach her. "There's a magic teapot, bringing a plant out of the bag, a hat stand, a mirror, putting them all on the wall so they don't fall off.
"There's a lot of pressure in that number, a lot of things to think about. So my brain is going 100 miles per hour. And then when that number's done I think 'right, now I can just have fun'."
The reboot of the stage production, which was first staged in 2004, is the latest instalment of a franchise which the public seem endlessly fascinated by.
Last year, a film sequel starring Emily Blunt - Mary Poppins Returns - took $350m (£273m) at the box office worldwide. A very healthy figure, albeit not as high as some of Disney's other recent hits.
Veteran theatre producer Cameron Mackintosh, whose group Delfont Mackintosh Theatres owns the Prince Edward, where Mary Poppins is playing, says they've been holding off for the right time to bring the show back to the West End.
"It's the first time the theatre's been available, so we had to wait patiently," he explains. "And also, Disney had the film last year and we would've been silly to confuse the public by bringing this back. We were on tour three years ago, and it was an enormous success, but we knew with the film coming out there was no point, we had to wait for the film."
The stage show also stars 86-year-old Petula Clark, who sings one of the film's most famous numbers, Feed The Birds. Supercalifragilisticexpialidocious and Chim Chim Cheree, naturally, also feature.
But there are new songs in the mix too, as well as characters who appeared in the books but won't be familiar to fans of the two films.
Mr Banks regularly refers to the stern nanny from his own childhood, Miss Andrew, who then appears later in the show to take over from Poppins, much to the children's horror.
Strallen says: "I want audiences to have not necessarily a new version of Mary Poppins, just a different one. People were open to the Emily Blunt version, and this one is actually quite true to the books. So it would be lovely if they went home and read the PL Travers books.
"[We have] Mary Poppins in the park, and the park keeper is introduced, and Miss Andrew is introduced, so we have all these different elements, and I think there's something about seeing magic live which is crazy, and you just don't get that from a film."
The show was awarded a rare five-star review by The Guardian's Michael Billington, who praised the "excellent performance" of Strallen.
"Every movement she makes is balletic - she doesn't just exit from a room but floats out of it with arms extended," he said. "Travers scholars may still miss the darkness of the books, but for the rest of us the show is an unassailable treat and Eyre's production has acquired the heart to go with its art."
However, Tim Bano of The Stage described the production as "muddled", adding: "Even at almost three hours, the whole thing feels rushed. The songs are taken at a lick, and the production jolts from one set-piece to another without pause for breath. Watch the film, read the books. Save the magic."
The book for the show was written by Julian Fellowes, who worked on the project several years before he became best known as the architect behind the phenomenally successful Downton Abbey.
"It was a rather interesting challenge, because you're having to be true to two sources as opposed to just one," he tells BBC News. "And you don't want to be disappointing for fans of the books or the film. My wife didn't even know there were books. But I enjoyed the challenge of it."
For Strallen, the themes of the show mean it could be staged "in Edwardian times, or in the future - it works at any time".
"Even though it's set in Edwardian London, it's about family, and it's about appreciating one another," she says. "And that is kind of timeless, it's at the core of everyone's life to love and appreciate each other.
Joseph Millson, who plays the children's father, George Banks, adds: "There are two things to this. There's a financial element that it just was time to do it again and the film went well. So there's all sorts of fiscal reasons for Disney and so on, but you know what, I genuinely believe this is a show for today, that could've been written this year and put on at the National Theatre.
"That's my feeling, that there's a genuine usefulness to it. Now of course people are here to eat ice cream and forget about their troubles, but honestly, the little bit that stays with you when you leave, is really useful."
Given how many theatres in the West End are owned by Mackintosh's group, is he at all worried about the state of venues in the West End?
"No, because we've done all mine!" he replies. "I'm just finishing the Sondheim, which is going to be glorious and it's completely rebuilt. So I've been doing that over the last 20 years, I've been rebuilding them, and they're the most wonderful places."
Mary Poppins is now playing at the Prince Edward Theatre.