Things got very stabby on Tuesday's America's Got Talent live quarter-finals when mentalist Colin Cloud took the stage to "solve the murder of Simon Cowell."

The brilliant mind-reader, who bills himself as a real-life Sherlock Holmes, invited Cowell to sit on a park bench on stage with him for a very complicated and slightly confusing demonstration of his skill set.

While the particulars of the performance are convoluted, the most interesting aspect came when Cloud invited Cowell's fellow judge and pseudo-nemesis Mel B to stand behind the acerbic judge and serve as the potential murderer.

WATCH: Simon Cowell's 3-Year-Old Son Eric Tries to Take Over His Job on 'America's Got Talent'

After calling a random member of the audience on stage to choose one of four colorful knives Cloud presented her, the impressive sleuth deduced that the volunteer had selected the white knife. Cloud handed the knife to Mel and asked her to stab Simon with it.

Needless to say, Mel had no problem going through with the act, but it turned out the knife had a rubber blade. However, Cloud had a rather surprising revelation: the white knife was the only fake knife of the bunch. If the volunteer had chosen any other blade, Mel would have (possibly) killed Cowell on live TV.

While the performance was undeniably impressive, the judges all pointed out just how unnecessarily complicated the premise of the act was. However, Cowell was still emotionally recovering from his (sort of) near-death experience when it came time to give feedback.

"I'm just sort of collecting myself a little bit at the moment," the shaken judge said. "I nearly got murdered on live TV."

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Cowell also pointed out that Mel didn't realize the knife was rubber and yet she was "prepared to kill me."

"Yes!" she yelled, excitedly.

"After last week, I don't blame her," host Tyra Banks added, referring to the pair's water-tossing spat that saw Cowell get soaked and Mel storm off stage.

WATCH: Mel B Goes Sexy in Sheer 'Superhero' Bodysuit, Gets Candid About Her Dating Lifeon 'AGT'

Mel spoke with ET after the show last week, and opened up about their argument -- which stemmed from Cowell making a crude joke about her wedding night. According to the former Spice Girls star, she only had one regret about their public spat.

"I just [wish] I would have had cranberry juice in there or something," she joked. Check out the video below to hear more from the judge about her rivalry with Cowell.