I ask because I just watched the MST3K take on "Soultaker" again last night. The 1990 film follows a group of teens who, following a nasty car wreck, all wind up disembodied souls on the run from a relentless soultaker.
The soultakers are of course creepy men in black with the power to suck the neon green soul right out of a coma patient. And our renegade teenage souls? Why they simply appear as themselves, only invisible to other humans in our material world.
What is a soul? It's largely a metaphysical concept: the immaterial and sometimes immortal essence of a person.
Science doesn't really weigh in on the matter, except (along with philosophy and psychology) in considerations of the mind-body problem. We struggle to comprehend the psycho-physical nexus between our immaterial consciousness/mind and this physical lump of brain.
For my part, I tend to favor the epi-phenomenalist viewpoint of Thomas Huxley. He was a dualist, believing that the mind and brain are not identical, but he also believed that the mind was an unnecessary byproduct of the brain -- a sort of cognitive shadow.
Now, I'm not sure to what extent they thought about all this, but the makers of "Soultaker" are essentially parallelism dualists. The comatose teen and the spirit teen are in harmony, but do not mutually influence each other.
From an epi-phenomenalist standpoint, I suppose those souls are just the shadows cast by their brains. And even as they miraculously exist separated from a brain-dead body, they can do nothing but conform to the shape they were cast in.
But what if they had taken the ancient Egyptian view of the soul or Ba as a human headed bird?*
Or, in keeping with Plato's Ideal Theory of Forms, what if they were idealized versions of themselves? The theory states that any reality we experience is just an imperfect image of an ideal. The classic example is that of a chair: Any chair we experience is a flawed take on the concept of an ideal chair. If you wanted to drag the brain into all of this, you could view our 3 pounds of skull meat as a lens through which the ideal nature of our soul/mind/consciousness is dimmed and distorted.
So birds, chairs or simply the boring teens they were in life? I have to go with the birds, friend.
* Just one part of the Egyptian soul cocktail, along with the Ka (lifeforce), khu (spiritual intelligence), sekhem (power) khaibit (shadow) and ren (name).