system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: when we are underwater, how does water not get inside our bodies through our eyes, ears, nose and every other orifice?
gpt
The eyes don't really have any openings for water to enter the body. Even the pupil is covered by a transparent cornea, it isn't just a hole into the eye itself.

Ears end in an eardrum that blocks the entire ear canal. If that is ruptured then there is a Eustachian tube that leads to the back of the throat.

The mouth can close, but the nose relies on the pharyngeal flap to block off access to the throat. The nose and sinuses could fill with water at the correct angle but not pass that barrier.

As for the other end, the anus is a sphincter which is a ring of muscle that closes off to prevent anything moving in or out. There are similar smaller sphincters in the bladder and the prostate to manage the flow of liquid in either direction.