Sun glints and luminous wriggles by the seashore

A rather delightful optical phenomenon, related to sun glints observed by the seashore, is illustrated: tiny spots of lights can be seen to move randomly in front of an observer wearing sunglasses with polarized lenses. On the seabed beneath the shallow waters, luminous wriggles can also be detected with or without sunglasses. By means of Fresnel equations, a plausible explanation of these two optical phenomena is given.