* Slow down. The speed of light is dependent on the medium it travels through. Denser materials have a higher refractive index, which means light travels slower in them.

* Bend towards the normal. This is known as refraction. The angle of the light changes as it moves from the less dense to the more dense medium. The angle of refraction is smaller than the angle of incidence.

* May change wavelength. The frequency of the light remains constant, but the wavelength changes to accommodate the change in speed.

Think of it like this: imagine a car driving on a road and then suddenly hitting a patch of sand. The car will slow down and change direction slightly because the sand provides more resistance. Light behaves similarly when it enters a denser medium.