The illusion is called “Lucky 13.”

That’s how many volunteers are plucked from David Copperfield’s audience and ushered into a cage onstage. The cage is then covered and hoisted into the air as the famed illusionist engages in some funny back-and-forth banter with the audience.

The trick ends when Copperfield tells the rest of the audience to turn around and say hello to the grinning, waving people who are most definitely no longer in the cage.

But Copperfield’s most successful maneuver may have come when he escaped financial liability after one of the “disappeared” people slipped and fell during a 2013 performance on the Las Vegas Strip — then sued the magician for millions.

A Nevada jury on Tuesday found the multimillionaire magician negligent, but said he wasn’t financially responsible for a British tourist’s injuries during the act, the Associated Press reported. The verdict means Gavin Cox and his wife, Minh-Hahn Cox, cannot seek monetary damages against the 61-year-old magician, the MGM Grand Hotel where he performs, or a construction firm that was performing renovations at the time.

But Copperfield didn’t emerge entirely unscathed.

On the witness stand in a Las Vegas courtroom, the man who has made an estimated $800 million performing illusions was forced to reveal the secret behind one of his signature tricks.

It basically involves flashing lights, lots of running and some confused kitchen workers.

As The Washington Post’s Travis M. Andrews reported: “Lucky 13” works like this: After the curtains drop over the cage, stagehands waving flashlights hurry the participants out — through dark and hidden passageways that snake through and out of the resort.

Everyone reenters the building via a kitchen. Then, they sneak into the theater from the back as everyone else’s attention is focused on Copperfield.

Cox said he and the other 12 participants had no idea where they were going, or that they would spend part of their evening jogging through service corridors of a Vegas Strip resort.

Some of those dark passageways were filled with dust and debris from the renovations, Cox’s attorneys argued, and someone — Copperfield, the hotel or the construction company — should have known what would happen.

During the dash, Cox fell and was taken to a hospital with a dislocated shoulder.

Later, he claimed he suffered chronic pain and said doctors found a lesion on his brain. He said his medical bills totaled more than $400,000, NBC reported.

Pictures of Cox, who had come to Las Vegas to celebrate his birthday, showed him in a hospital bed under a blanket, his right arm heavily bandaged.

“Seeing David Copperfield was the highlight of a dream trip to celebrate my 53rd birthday,” he said, according to the Sun. “Instead, it turned into a nightmare. My health has been wrecked, and I’ve lost my business and my life savings.”

As for that meandering dash from the cage to the back of the theater, Cox’s attorneys likened it to an obstacle course — a dark route in which the floor changed from carpet to cement to linoleum.

The alley, Cox’s lawyers argued, was coated with construction dust.

Over five years’ of legal wrangling, Copperfield fought a battle on two fronts.

He wanted the jurors, or whatever other legal authorities there were, to believe that he was not responsible for Cox’s fall and injuries.

He said he had even walked the path a few minutes before Cox did.

But the illusionist also tried to convince a judge that he did not have to reveal the secrets of his trick.

“It’s not just tricks,” Copperfield said in 2013, something he has repeated over the past half-decade as his attorneys argued the trial should be closed to the public. “Secrets and lots of hard work go into this.”

But the judge disagreed, arguing that if it was a secret, it wasn’t a particularly well-kept one.

Copperfield has performed the trick with 55,000 participants over the years, according to NBC.  Every one of them is well aware of what happens when the curtain is dropped over the cage.

And now, so is the rest of the world.

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