There are only thirty students in this classroom. But I know one more person among us.
The unknown "thirty-one". Nobody notices him, nobody can see him. But I know he is there, blending in the background, observing from close proximity; and I know he pretends to be one of us. When our eyes keep catch each other, I don't know what's the meaning behind his faint smile. Nor I know what his dark eyes can see.