A pigeon’s head does not actually bob back and forth. It locks in place, then jumps forward. High-speed video breaks every step into two distinct phases: - Hold phase: the head stays almost perfectly still relative to the ground while the body keeps walking forward underneath it. The neck extends and then compresses like a telescoping stabilizer. - Thrust phase: the head snaps forward to a new position ahead of the body, faster than the body is moving, and locks again. From the side it looks like a nod. Relative to the world, the head moves in a stop-and-go pattern, not a back-and-forth one. Why do it this way? - Pigeons have eyes on the sides of their head and very little binocular overlap, so they rely heavily on motion cues instead of stereo vision. - During the hold phase the retinal image is stationary. That makes anything moving in the scene, such as a predator, a rival, or food, stand out sharply against a frozen background. - During the thrust phase the head moves quickly,...