The terms refer to how a person perceives certain things.
"a psychological phenomenon in which the mind responds to a stimulus usually an image or a sound, by perceiving a familiar pattern where none exists".
So it easy to see things that are not really there. The most famous ones can be water stains on wood that can form a face, clouds that look like rabbits, etc.
Remember the 'Magic Eye' pictures and books?
The term refers to the relationship between or among reality, symbols and society.
The dictionary defines simulacra as:
"something that looks like or represents something else".
The Latin meaning (from the word 'simulacrum') is:-
"Likeness, image, representation, form or portrait".
Face on Mars...
Man in Moon...
Skull in Decaying Rose...
In the modern world of media, cultures can often play a part in misrepresenting or misinforming on aspects of things that can or do look like something else... and human nature our brains can perceive them to be something that they're not.
So it's with the above possibilities that everyone must be aware that "nothing is quite what it seems" and that what some might suggest are ghosts, spirits... or they see a shadow, etc. it might... just might... have a rational explanation.