altering the angle of each line very slightly

Posted by Elinor on 2011/4/3 22:55:22

"A simple way to demonstrate the illusion of motion is to draw a line in the lower right-hand corner of each page of a pad of paper, altering the angle of each line very slightly in a single direction. If the pages are then riffled at a rather fast pace, the eye will perceive the illusion of a moving line."



What does it mean? Is it a curvy line or a straight line?


Thanks.