Ouch! Marc Salem has just brought his hand down on an upturned knife, and now there’s blood seeping through his bandages. This is not, it turns out, part of the act. Indeed, this calamity has befallen him only twice, he assures us — both times on opening nights. Perhaps unnerved by having brought a cognitive therapist out of the crowd to help him with his trick, he’s guessed wrong which of the three upturned polystyrene cups concealed the dangerous blade, and the bloody consequences are there for all to see.

Ah well, a trick going belly-up isn’t fatal to a show like Salem’s. In fact, much like finding a cherry stone in a cherry yoghurt, it’s proof that there’s something real at the heart of his mix of (as his English equivalent, Derren Brown, would have it) magic, suggestion, psychology, misdirection and showmanship.

Before knifegate, the suited New Yorker has shown off his mentalism to impressive, if not entirely winning, effect. He’s memorised a pack of cards in seconds. He’s correctly — and entirely bafflingly — predicted in a sealed envelope the exact appearance of a volunteer culled seemingly at random. Best of all he’s zoned in on people’s “tells” — the physical and verbal cues that show when we’re lying — to read minds while alerting us to the process too.

Five years after he first made jaws drop on this side of the Atlantic, he’s finally given his show a serious overhaul. Unfortunately, some of the new cons are either a bit murky — a Deal or No Deal set-up, with £20,000 on offer to anyone who outfoxes Salem, plays too fussily to be as interesting as it sounds — or convolutions of earlier, stronger tricks.

There’s still plenty to be dazzled by — particularly his long-standing finale, in which, blindfolded, 50p pieces taped over his eyes, he tells audience members about holidays they’ve been on and objects they own. But his eye-opening ideas about influence and suggestibility are largely confined to the programme notes, leaving him too reliant on the sort of patter that jolly dads try out on recalcitrant 12-year-olds: “Have you ever taken somebody’s pulse? Did you give it back?”

Mind you, tough crowd on opening night. Why pay good money to see a magician and then act all surly when asked to participate? Miserable bunch. It is, of course, Salem’s job to turn a group of awkward individuals into a rapt audinece, and his low-key showmanship isn’t always up to the job. But there’s good stuff in here, which tightly folded arms do nothing to unlock.

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