I just don't understand

It’s a puzzle that I don’t understand.

How do they have 1 block left over, while still ending up with 4x6 rows?

What obvious thing am I missing?

Mouseover space

The final version is not a full 6 blocks tall, it’s just a little shorter all the way across, which adds up to the equivalent of one block total left over.

You have to look really carefully, and compare where the little partial blocks join. I can’t explain it any better than that.
Roddy

It’s this puzzle chocolatified. A subtle illusion of angles.

There are many variations of this trick, some of them artistic and amusing. The great puzzlemeister Sam Loyd had an interesting version called the “Get Off The Earth” puzzle.

It was like a circular slide rule, with a rectangular cardboard back piece, and a circular cardboard front piece, riveted at the center so you could rotate it. It had caricature pictures of several “Chinamen” on it, drawn with part of them on the back piece and part of them on the central disk. When you rotate the disk, the pieces of the pictures align differently, and one of the “Chinamen” disappears.

Discussions, with pictures of the thingy:
http://www.jimloy.com/puzz/getoff.htm
http://britton.disted.camosun.bc.ca/jbgetoffearth.htm (with animated GIF!)

I never would have thought of doing it with chocolate. Brilliant, because it’s something everyone is familiar with and that comes with nice clear rectilinear lines. And it tantalizes with the idea of an infinite source of chocolate!

No, it is very different.

The “missing square puzzle” is based on the fact that two (red and blue) triangles have different slope angles (2/5 and 3/8) but close enough to be overlooked without looking closely.

This chocolate puzzle is just cutting a (constant slope) diagonal and shifting everything sideways so where you had 1 x 1 squares now you have 4 “squares” with lesser height. It would be very obvious if done with exactly marked paper but with chocolate the squares are not so clearly delimited and admit more fudge. _

This is the same as the vanishing leprechaun and the old trick of cutting X money bills and getting X+1 money bills (which are imperceptibly smaller than the originals). This is the reason the money bills have the same serial number printed twice, to prevent this trick.

OK, so I totally got the OP’s one right away. (The remnants of the diagonally sliced boxes make up a little less than one block, which is then removed. The line through the sliced ones tricks us into missing the fact that they are now shorter.)

But even after reading the solution to the leprechaun one, I’m still not getting it. If you count the heads, a new one has definitely shown up.

And if you count the bodies there is one more. If you read the entire page at the bottom is a link to the explanation: http://britton.disted.camosun.bc.ca/jblep3.htm

None of the 15 has a whole head. The heads are a bit smaller after than they were before. Try counting noses, instead: Leprechaun 11/15 is missing a nose.

Get off the Earth: http://britton.disted.camosun.bc.ca/jbgetoffearth.htm