In this scenario I'm a teacher and pupil is a pupil, a student. This pupil is someone I've laid my eye on, not in a pervy way but in a good student way. This pupil has a great future ahead. My "eyelid" is a lid for my "eye" pupil, meaning it's the door of my classroom.
So I close my eye and the fly goes from over the student to under the classroom door. Problem solved.
EDIT: lol, posted this on the Madeleine McCann thread at first