- How did Myrtle cover her eyes when Harry entered and left the prefect's bathroom? The book says that she covered her glasses, but aren't her hands see-through? I think Harry may not have gotten the privacy he thought he had.
This raises some fun questions about ghosts in general. Like, how come if they are see-through, you cannot make out their inner organs? Well a reasonable answer is there aren't any, the ghost form merely replicates the outermost shell.
Let's think about Almost Headless Nick in this context. You can certainly see the gore at his wound when his head is dangling, but (presumably) if the head is in position, it's impossible to see the wound in the inside of his throat; only the outermost shell is replicated in the world and thus when covered up, the wound ceases to exist.
And now back to Myrtle; once she covers her eyes, you cannot see them anymore through her hands. Her eyes literally cease to exist during the time they are covered and thus she is unable to perceive anything with them.
I like the way of answering the question because of how quietly unsettling it is.