With red and white light, the shadow of the object appears in the complementary color -- cyan -- and the shadows change as your angle of vision changes.

CNN: What the brain draws from: Art and neuroscience

He is following a simple rule: Keep the angle of the falling ball constant in your vision and adjust your running speed accordingly.

WSJ: Matt Ridley on Gut Feelings and the Writings of Gerd Gigerenzer | Mind & Matter