Why does a wart turn black after you freeze it?

When a wart is frozen, the extreme cold causes the blood vessels within it to constrict and eventually die, leading to tissue damage. This process can result in the wart turning black as the cells break down and the tissue necroses. The black color is often due to the formation of dried blood or the breakdown of cellular components. Eventually, the wart will fall off as the body heals and new skin forms.