Today’s illusion has a pretty interesting effect. We have featured several animations that are similar to this one (see the Turning Wheel Optical Illusion and the Spinning Dancer Illusion), but I still find the effect to be very fascinating. The train in this animation is moving at a constant rate of speed. But what direction is it moving? When you first look at it, you will perceive it as either moving toward you or away from you. If you watch the train for a little while longer, you will find that it changes directions. Keep watching and see if you can get the direction that the train is travelling to flip-flop back and forth.