Showing that the angles that the incoming and outgoing light make with the surface are equal.
What happens when the apple (big red dot) is covered by a piece of paper? (just like the viral tiktoks of people holding up paper to mirrors and asking how the mirror "knows something is behind it").
Can you ever move the eye (blue dot) so that it can see the apple? What direction should you move the eye?
What if the apple was covered on all but 1 side? Could the eye ever be moved so it can see the apple now?