Parallelogram Illusion

The red lines do not appear to be of equal lengths, but they are. Checking the "Show hint" box helps with overcoming doubts.

The brain dissects the picture and attempts to interpret it into distinct separate objects, as is the case with, say, Kanizsa triangle. It recognizes two parallelograms -- one smaller, the other bigger -- even when the midline is not present. All parts of the bigger parallelogram appear begger by association.