You might claim that "The 12- or 13-Man Brain Teaser" is waaaaay more straightforward than I'm making it out to be.
"Look," you might say, "You have 12 men in the first picture. You split them into 24 halves and recombine 22 of those halves into 11 people. Then — and this is the entire trick — you point to the remaining two halves and claim that they're full people: 11 + 2 = 13 men. In the final configuration, the two 'half men' are #1 and #13, each of which gives up a half and doesn't get one back."
If you're making this argument, you're absolutely right: That's how the trick works in principle, as I said in giving the illustration of lines (on the previous page). But you'd be ignoring the key element that makes "The 12- or 13-Man Brain Teaser" different from that page's line example.
If you bisect a line, you can truthfully call each of the resultant halves a "line." But if you cut a person in half, you can't claim that you haven't really done anything; each of the two halves is a person itself. (Believe me: When I used this line, the police weren't impressed.)
"The 12- or 13-Man Brain Teaser" is extremely baffling because each of the final 13 men looks like a full person, even the two "half-men." And it's not just #1 and #13 that are involved: if you were to take the missing half of #1 and the missing half of #13 and put them together, one of our men in the final configuration would consist of nothing more than a scalp on a pair of feet.
No, all the men are altered! And luckily for you [having read this far], here's an image that shows how all the images have been altered.
Basically, the puzzle works by cutting each person in two, taking a small slice of them (1/12 of their height) and passing it over to the right until, after connecting 12 people, you end up with one entire extra person. However, the creator mixed up the order of the people — Arrrrgh! — so that you wouldn't easily see what he had done. ( : - )
Full credit for this brain teaser, along with all the images, must go to the proper source — NOT me! Credit (and appreciation) goes to Matthew Baldwin of Defective Yeti. "Thank you, Matthew!"