If Kiera stands with her back against a smooth, flat, and very high wall on a sunny day, facing her friend Leon who is 10 meters away from her and facing the wall, and there is no other object around to cast a shadow, what will Leon see on the wall behind Kiera as she waves to him?

Provide a very brief response.
Leon will see the shadow of Kiera's waving hand on the wall behind her. The sunlight that travels in straight lines will be blocked by Kiera's hand as she waves, causing a shadow of her hand to be projected onto the wall. As Kiera's hand moves, the shadow will also move in sync with the hand movements, allowing Leon to observe the waving motion as a change in the shadow's position on the wall. The shadow will be visible to Leon because the wall provides a continuous, unbroken surface that captures the outline of the shadow clearly, and no other light sources are present to dilute the distinctness of the shadow.