This optical illusion has many lines that are going the same way, as if they are bent, which is the effect of parallel straight horizontal lines. Alternating white and black bricks form these lines to appear bent, but when you look closely at the lines, they are straight. It's because of the different positions of the white and black bricks that make the lines seem bent. The line in between each row has to be a shade of a color in between the dark and light colored bricks for best result. The brain uses those two different colored bricks and their different positions in each row to make it seem that the rows are bent, but they are completely straight.
"BrainBashers : Optical Illusions." BrainBashers : Optical Illusions. N.p., n.d. Web. 18 Mar. 2015.