Eureka (n.) comes after you've stopped trying, so it gets credited to luck.
Eureka (n.) is followed within a minute by checking whether someone already thought of it.
Eureka (n.) is like a key turning after an hour of jiggling, and you remember only the click.
Eureka (n.) is the shout that arrives after hours of looking stupid.
Expressions given off (n.) is a non-controlled facial movement or expressions that are given off while that person presents himself.
Facial expression (n.) exists only within a play of the features; someone who had seen only sad faces could not sense them as sad.
Facial expression (n.) can be the same on two faces, yes and no; to say what kind of strange smile, one might have to draw the face.
A Facial expression (n.) is noticed only when the face changes; a face that always smiled would show its smile as mere anatomy — expression lives in the play of features.
A Facial expression (n.) is something seen, though the same lines in another picture can look quite different.