Of course, even in movies where it was all done the “honest” way, they still (usually) have the luxury of doing many takes, and only keeping the one where it worked best.
(I say “usually”, because sometimes a take is really expensive, like the burning of Atlanta in Gone with the Wind)
Even if it’s all one unbroken shot, shortly before panning up to Newman’s face those hands we’ve been watching leave the shot.
Why?
It’d be slightly more impressive if the hands remained in the shot until the pan up — and I say “slightly” because, as you say, it forced you to conclude that it’s Newman, and, well, (a) that’s pretty good, by which I mean (b) it was good enough. But the only reason I can see for those hands to leave the shot is for a practical effect, like you’re kind of on about: they don’t need to stop the camera or anything, they can just have the other guy (wearing a shirt with similar sleeves) stop messing around with the cards and move away right as Newman swaps in.
Yes, and after watching the clip several times, I notice the hands rolling over the cards to expose the faces are noticeably not as deft as the hands that preformed the preceding tricks.
Still, I never would have suspected this just watching the movie, as was intended.
This doesn’t jibe with my recollections – and I’ve watched the scene looking for precisely any such shifts. I’ll watch it again to make sure, but I don’t recall the hands leaving the shot.
Just watrched it on YouTube – There IS a very short time when the hands both withdraw.
Clever
It’s not hard to learn to manipulate cards. I did, and back in the day, I was a reasonably good card sharp. But it took a lot of practice. And I mean a lot.
I have no doubt that Scarne was involved somehow, even if nothing more than to teach Newman how to manipulate the deck. That wouldn’t take long, but Newman would have had to devote hours to practice, in order to be able to do what he did as quickly as he did.
Agreed, as I said above.
But the momentary disappearance of both hands from, the frame makes it very possible that Scarne (or someone else) did the actual card handling. In fact, the way the handover could have occurred – one hand on one side of the uptilted deck, followed by hand disappearing, folowed by opposite hand reaching for the other side of the upended deck --makes a pretty natural set of movements that subconsciously suggests that it’s the same person doing it all, but providing the opportunity for a quick switch.
I’ve just watched the scene again on youtube and I think there is a cut after he fans the cards out, just before the camera pulls out to show Newman. But I could be wrong.
I’m not sure it counts but the B&W 1931 film version of Dr. Jekyll and Mr. Hyde used color makeup and matching color filters to show the transformation on screen.
"… Newman actually did one of the moves himself. Or should I say he did half of one of the moves?
Which one? It’s called the ribbon-spread turnover, and in the film, a close-up shot of Scarne’s hands shows Scarne spreading the deck on a table. But once the deck is spread and Scarne’s hands are out of the shot, there’s a noticeable splice just before Newman’s hands come into view and finish the move by turning over the deck with a flourish."
The “noticeable splice” occurs around the 32 second mark of the link in post #24. It might be more noticeable if the clip had better resolution than 480p.
Another practical effect is the Pepper’s ghost illusion, which uses a reflection on glass and lighting tricks to make something appear. (It’s the effect used in the Haunted Mansion ride at Disney World to make the ghost appear to be in your carriage.) The Wikipedia article says the trick was used in the movie Home Alone to make Joe Pesci’s hair appear to be on fire from the blowtorch.
I don’t think it quite fits the definition of the OP, but it’s a neat trick. The first stage of the transformation (shadows under the cheekbones, bags under the eyes) was done with red make-up. When lit with red light, they were invisible to the black-and-white camera. When they changed the color of the light, the changes suddenly appeared, in-camera, without interrupting the actor’s performance.
I can do the ribbon spread turnover. Well, I could; it’s been years since I last did it, to be honest. The trick—and there really isn’t one—is to get the spread just right. Get that right, and you can do the turnover all day long.
Thing is, you need a felt surface, or at least a tablecloth. That gives the cards something to dig into, so they retain their ribbon spread, no matter how many times you perform it.
Ditto in The Return of the King when Gandalf rides Shadowfax onto Denethor’s pyre to rescue Faramir.
Of course, it’s also possible that he did it, but he didn’t do it as quickly as he did it. They could have changed the camera rate for the tricks, and changed it back before we saw his face: That wouldn’t leave any visible seam, either.
Clever, but it only worked on black-and-white film. To a live audience, the color changes would have been obvious.
Those would both have still been somewhat risky stunts, if that was the full extent of it: An optical image of a fire will emit just as much radiant heat as a real fire (though you’ll at least avoid the convective heat and hot embers and the like).
If the audience was entirely composed of color-blind people, it would work! 
I think it makes it a virtual certainty.
If Newman had done the fancy shuffles, all in one uninterrupted shot, it would have been crystal clear. What a “holy shit!” scene it would have been. Hell, they’d have panned (is that the right word?) up to his face.
As it was, they used a clever, likely-to-miss switcheroo when the hands leave the shot. Really effective, clever filmmaking.
Not really – I considered mentioning this effect – which obly works in black and white – but it doesn’t really fit because even colorblind people wuldn’t see it.
The effect is very clever and inexpensive (and impressive), and has been used countless times. It’s used in the 1925 Thief of Bagdad and in an episode of the original Twilight Zone.
For a practical application of a similar effect: Some roads have different speed limits at day and night, and you can use one low-tech sign to display both speed limits, by using the appropriate sorts of paint: The day speed limit shows up on the sign when it’s illuminated obliquely by daylight, while the night speed limit shows up when it’s illuminated by car headlights close to where the observers are.
Newman could have learned those shuffles and so on. I did.
I’m not any kind of a card magician. But I am the person you don’t want to play cards with. Let’s leave it at that and ask no more, shall we?
Is that a theoretical, or is it actually being done, and if so, where? Can you provide more detail?