The "whole triangle" looks like it has a height of 5 units in length and a base of 13 units in length. 5 x 13 divided by 2 should give us the area, 32.5 square units.
But the pieces are:
12 units = red
08 units = green
07 units = yellow
05 units = turquoise
-----------------------
32 units
I'm guessing that the illusion of giving and taking a half square unit both ways is what causes a whole square to appear to be missing. Or something.
Anyway, did you give Revned his cookie yet? What kind of cookie is it?