沖涼所見的

沖凍水涼凍到縮埋左XD

睪丸(Testis) is inside the scrotum (spring pocket). It needs a lower temperature than the body temperature in order to function well, i.e. to make sperm. When you are bathing, the scrotum and testis expose to a lower temperature, the contraction of the scrotum will elevate the testis in order to keep them near the body. As it goes closer to the body, the better the temperature it can function.
Therefore, it is a normal phenonemon to see the scrotal skin contraction.