During a solar eclipse, why do Baily's Beads occur, and what does this phenomenon illustrate about the Moon's surface?

Baily's Beads appear when the Moon’s uneven rim lets small slivers of the Sun shine through its mountains and valleys as it covers the Sun. As the Moon moves across the Sun, sunlight can peek through the deepest valleys, creating bright points that look like beads. These beads appear and disappear quickly, showing that the Moon’s edge is not smooth but has many peaks and troughs. The pattern of the beads tells astronomers the exact shape of the lunar limb and confirms that the Moon’s surface is cratered and rugged. For example, when the eclipse began, observers saw beads flicker along the Moon’s edge, revealing the jagged profile of its terrain.