There is an intruiging concept called the “Uncanny Valley”.
It is the primal feeling of ‘wrongness’ one might get when seeing something that is not exactly humanoid, but quite similar.
For example, the latest versions of humanoid ‘customer service’ robots (sadly, you probably know exactly what kind of dolls I’m also referring to), or CGI-recreations of (deceased) actors.
De-ageing someone digitally can give the same effect in almost all cases.
We as a species can almost immediately tell they aren’t “real”, even though they’re specifically made or modified to resemble us, with the technology to do this getting better pretty much every year.
This Uncanny Valley effect is quite common in those scenarios, thanks to the Human pattern-recognition ability.
What makes this extremely unnerving is that this phenomenom predates AI, CGI and similar technologies by many, many years.
Charles Darwin wrote about a similar concept in 1839, which is the earliest official publication I could find.
However, consider the plethora of myths, urban legends, folklore and similar stories told throughout the ages.
There have always been sightings of creatures that are humanoid, human-like or just vaguely human-related.
We keep evolving, changing and developing, yet the Uncanny Vally remains.
What is it that our ancestors saw? What is it we see? What are or were we afraid of?
Are you sure you know what you saw vanish from the corner of your eye was just a shadow?