Learn about tangent vectors in this video (5:54) from NOVA Digital. In this hypothetical world, zombies always move straight toward humans. This means that the tangent vector of a zombie's path points at the intended target. However, when the human moves, the zombie's tangent vector points to where the human is at that instant, not to where the human is going. The zombie is not smart enough to move toward where the human will be. Therefore, the zombie takes a longer path, giving the human the chance to get away. If the human moves faster than the zombies in a circular path, multiple zombies will eventually converge on a smaller circular path that follows the human's path.