* Light doesn't actually speed up when it moves from a denser to a less dense medium. Instead, it changes direction. This phenomenon is called refraction.

* The speed of light is constant in a vacuum, which is the fastest it can travel.

* In denser mediums, like water or glass, light slows down because it interacts with the molecules of the medium.

* When light moves from a denser medium to a less dense one, like from water to air, it speeds up again, but it's still slower than the speed of light in a vacuum.

* The change in direction (refraction) is what makes light bend when it enters a new medium.

Think about it like this: Imagine you're walking through a thick forest, then step out onto a smooth, open field. You'd move faster on the field, but the direction you're walking might change because of the transition. It's similar to how light behaves when moving between mediums.