I spotted something really bizarre in the short film "A Nightmare"/"Le Cauchemar" from 1896 by Georges Méliès. You can read a summary of this very short film here or here, or watch it on one of the great Georges Méliès DVDs. (I watched it on this one.)
The crazy thing I found is, in the final scene, when we cut back to the original bedroom, Méliès' groin area is hand-blacked out by spotty marks. I am not trying to be a wise guy. You can see it in the last screen grab in this rotten tomatoes review. Here is the photo for convenience:
(click to enlarge)
But it is even more evident when you watch it on DVD, especially if your DVD player has a zoom feature, because the black dots are clearly hand-drawn on every frame—they hop around erratically (almost like they're animated...!). In the prior scene, this character had jumped around acrobatically, and possibly this is where some piece of fabric came loose. They had to do a camera stop where the actor (Georges Méliès himself) froze in position on the bed while the set is changed around him. In the finished film it is jump-cut together so that the background disappears instantly and he is awakened from his nightmare, back in his bedroom.
He is wearing sleeping underclothes, and maybe one of these two scenarios occurred: 1) Out of propriety, an exhibitor from way back when, or someone who owned the film print at some point in history, blacked it out because maybe there was a bulge they found offensive 2) Méliès (or his team) blacked it out on all prints (or the negative) because his flap had accidentally fallen open, leaving him exposed.
If it's the latter, you may ask, why wouldn't they reshoot? If you look at how exactly the match cut is of his body position between these scenes, perhaps this was the preferred solution (the screen grabs here don't show this—you have to watch the film). This is 1896, and Méliès is discovering and mastering new film techniques, and my guess is that replicating this special effect cut may have been daunting compared with simply blacking out the offending region. He had to freeze himself in a very awkward position (legs in the air) in the bed while his crew rearranged the set, until they turned the camera back on.
It was apparently quite hurried because you can see the remnant of the prior "nightmare" set on the right of screen which has not been properly covered up by the new set. Compare the before and after shots below. The bed (looks like a wheelbarrow) is in the exact same position in the frame, and the remnant of the first set is visible on the right side in the second frame grab.
Some film historian should be put to work to answer this important question! For instance, if all the existing film prints have this blacking out, then it likely originates in the negative. But if there is a "clean" print out there, then we can look at what was blacked out and make a guess as to why.