The Great Animal Crackers Doppelganger Mystery

The opening preamble
I'm going to tell you something you almost certainly don't know about the Marx Brothers.
No matter how many times you've seen Animal Crackers, chances are there's a huge amazing thing about this film that you have never spotted.
It's true I have told some other people. I wrote to tell that chap who was Freedonia Gazette's British representative, forget his name now, Ray something I think, but for some reason he didn't believe me. He was an optician, if I remember rightly: a naturally sceptical breed of men. Then I wrote it up as an article and sent it to Paul Wesolowski, the Gazette's head honcho; he forwarded it to Gummo's son, presumably on the grounds that there was nobody else less likely to have an opinion about it, and shortly after that the Gazette folded. (Coincidence?) Flushed with triumph I wrote to Glenn Mitchell, author of The Marx Brothers Encyclopaedia. I knew I was definitely on to something when the letter came back because I got the address wrong.
So here it is.
There is an entire scene in Animal Crackers in which the Marx Brothers are doubled by three other men.
This is not mere opinion. There is no doubt.
Once you notice it, it is impossible to deny it.
The scene is the one where Chico and Harpo are stealing the painting in the dark, in the presence of Groucho and Margaret Dumont.
From the time the lights go out to the time they come back on again, Harpo, Chico and Groucho are not Harpo, Chico and Groucho but three other geezers miming to Groucho and Chico's dialogue and trying, and pretty much failing, to move like Harpo, Chico and Groucho.
Go away and watch it again. Look at those strange figures, weird figures. Who are they? Why are they there? Time to use the Sherlocka Holmesa method.

How can we be sure of this?
I'm very glad you asked me. There are a number of giveaways. First, even if you think they are the bona fide boys, they are plainly miming. Their physical gestures are forced and overt in order to match the dialogue, which they sometimes anticipate. When Groucho asks if anyone is there and Chico replies, 'Groucho' turns to Dumont (who is the real Dumont by the way) and nods slowly for ages while he waits for the soundtrack to catch up with his actions. Look at Harpo - big, bulky, slow 'Harpo' - flapping his arms when he's hanging from the painting. 'Chico', too, makes a bunch of strange, slow gestures completely unlike his normal self.
Second, there is the fact that when the lights come back, they do not simply switch back on. The scene goes from twilight to pitch black - for no logical reason at all - before then cutting to full illumination - with the camera in a totally different position.
Finally, there are the men's faces. These are to be found on the front of their heads and remain today as useful a means of identifying them as they were back in 1930. Okay, it's pretty dark, but we get a good look at 'Harpo' when there's a lightning flash (freeze-frame it) and 'Groucho' is discernible throughout. Look at his little head! Look at his close-cropped hair! Groucho has a sharp centre parting and fluffy hair rising up in a v-shape in this movie. Does this guy? No. He looks like Leonard Zelig.

Okay, then - why?
Here we can only speculate. In roughly reverse order of likeliness, here are the possible explanations I've come up with.
First, recall that this is the film in which director Victor Heerman supposedly had cells built and brought on the set so as to ensure the Marxes could not escape between takes. This story is probably apocryphal, but the point of it - that it was genuinely difficult to get all four Marx Brothers on set and doing what they were supposed to be doing at the same time - is backed up by the testimony of just about everybody who worked with them. Could this scene have been shot on a day when they were AWOL, on the grounds that it was dark and nobody would be able to see them properly anyway?
Or maybe it was planned that way from the first, as a scene that didn't need the real Brothers on set, because it was dark and nobody would be able to see them properly anyway. This would mean that 'they' would most likely be miming not to the soundtrack we hear but to crew members reading the script off-camera, adding to their obvious physical dislocation; with the Brothers' dialogue added later. Presumably it was felt that this wouldn't matter too much because it was dark and nobody would be able to see them properly anyway.
Or, perhaps the original shoot proved unsatisfactory - maybe the light levels were wrong and the film came back from the chemists more or less pitch black. I'm speculating wildly here. Then, when a reshoot was ordered, it was decided not to bother recalling the Brothers themselves on the grounds that the soundtrack didn't need re-recording, and it was dark and nobody would be able to see them properly anyway.
Or, maybe the early sound recording techniques were still so cumbersome, that no opportunity to get round them would be missed. So here we have a scene in the dark - why use live sound when you can't really see the lips move? Get the boys to record the dialogue, then they can mime to it without the sound department needing to get in on it at all. And then, why use the Brothers at all? After all, it's dark and nobody would be able to see them properly anyway.

Okay, then - who?
Well I had no idea until recently. I always assumed they were just anybody, perhaps the people stood nearest to the set at the time; especially since you could throw a brick from a moving bus and hit someone who looks more like Groucho than this weedy little guy. But then I saw a sentence in Simon Louvish's book, in a paragraph with nothing whatever to do with this scene, that leaped out at me.
He writes: "Like all stars, the Brothers had doubles, to set up the scenes, till they were required."
That's not identical doubles, of course, just reasonably similar stand-ins. And that's who they must be.