Since i can’t post in that forum, i’ll just post here. =)

What you have there is a set of 12 guys, that are divided by a horizontal plane(HP) gradually.
One guy is divided by the HP just at the top of his head, then the next just in the middle of the face, then in the neck, and so on.

I’ll ilustrate this division like so, 1/12 ilustrates the guy that has just a bit of the head cut off(the 1) and the rest of the body bellow the HP. A 6/7 is a guy that’s cut more or less in the middle, 6 is the part of his body that is above HP and 7 the part that is bellow.

1/12
2/11
3/10
4/9
5/8
6/7
7/6
8/5
9/4
10/3
11/2
12/1

What they did was:

…/12
1/11
2/10
3/9
4/8
5/7
6/6
7/5
8/4
9/3
10/2
11/1
12/…

So now you think you see 13 guys, but you’re actually seeing 11 complete guys, and 2 (the first and the last)that have part of their head shaved off and other that has part of his shoes shaved off. =)
You’ll notice that the guy more on the left, loses part of his head, and the third guy from the right, loses part of his shoes.

You probably all noticed that all the guys look a bit shorter when there are 13, and their heads look a bit smaller, that’s because they are no longer 1+12=13, or 6+7=13, or 8+5=13, but are instead just 12.

Btw, the reason why it’s so hard to see this is because the guys are mixed together, i mean, the 1/12 guy is next to what i think is the 4/9 guy, and the 2/11 guy is next to what i think is a 7/6 guy, they are not ordered, so it’s hard to notice it. =)

I love puzzles! ^_^