So when we swim, we can make water not enter through our nose and mouth, simply by holding our breath. However, the mouth and the nose aren't the only cavities. What about the anus and the genitals? They obviously can't "hold breath", so how do they stop water from entering?
I thought the reason is gravity, but then, people would be killed when diving because your butt is facing up, against the gravity.
Another explanation might be that the internal pressure is higher than the external one, but I fail to recall any organ that creates the pressure..