Ok ChatGPT, explain it for children:

ChatGPT A preauricular sinus (PAuS) is like a tiny hole near your ear that you’re born with. It can be on one side or both, and sometimes there can be more than one hole on one ear. People have known about these little holes for a long, long time, even before doctors named them. Some artists in the past, like Hieronymous Bosch, drew pictures of them. Doctors later called them preauricular sinuses.

These little ear holes are special because they can be a part of different health conditions that some people have from birth. Think of them like a unique feature, just like how some people have freckles or dimples. So, in modern times, doctors see them as something interesting about a person’s body, but they also check if they might be connected to any health issues.

A much easier read: https://www.cornwalllive.com/news/uk-world-news/people-born-tiny-holes-above-811203
TL;DR: it’s called preauricular sinus and is thought to be vestigial gills

I’m trying to wrap my head around “invagination”. Like I’m pretty sure I get the general gist of the meaning, but it’s really making me realize I don’t think I know the etymology of the root word at all…