The Mueller-Lyer Line Length Illusion!
The Mueller-Lyer illusion
takes advantage of processes that the brain uses to judge depth and distance.
On the next screen, watch the numbered pairs of lines, and decide which pair
of lines are equal in length. To make it harder, wings have been added to the
lines, some facing in and some facing out. For instance, observe the obviously
unequal lines below. Only the red portions count.