David Copperfield was forced to break the magicians code in court Tuesday, when a judge ordered him to explain one of his most famous tricks following a lawsuit from an injured participant.

British tourist Gavin Cox, 58, is suing the illusionist for negligence after he claimed he was injured after taking part in Copperfield’s “Lucky #13” trick in Las Vegas in 2013, the BBC reports.

Cox said he has suffered chronic pain and brain injury following a fall that dislocated his shoulder. He said in the suit he has spent more than $400,000 on medical bills, according to NBC.

Copperfield, who is the world’s highest paid magician, has performed his famous “Lucky #13” trick thousands of times without prior incident. The performance involves randomly selecting 13 audience members, making them disappear on stage, only for them to later reappear at the back of the room.

A Las Vegas district court rejected Copperfield’s defense, which argued that disclosing the secret behind the trick would be financially detrimental to him. He was ordered to explain how the trick was done.

The reveal (spoilers)

Copperfield’s executive producer explained in court that, once the curtain falls, the 13 participants brought on stage are taken through passageways that go around the Las Vegas MGM building, where they exit and re-enter at the back of the theater.

“There was a duty by the defendants to provide a safe environment to the audience participants,” said Cox’s lawyer, Benedict Morelli, in the opening statements. Cox said that the passageways were full of construction dust and debris.

Copperfield claims the passageways were clear when he walked through them. MGM, who is also a defendant in the lawsuit, concurs.

Copperfield will testify on Tuesday as the trial continues.

Contact us at letters@time.com.