I put banana peel in the teacher's way so they trip and fall and snag a bad concussion; Then I pull the fire alarm so the teacher is soaked so they have to run home and we can leave within 15 minutes; Then I hand the teacher a block of exploding TNT so that they can't come to class! 5 MINUTES BEFORE THE 15 MINUTE MARK, THEY WALK IN! WHAT ARE THEY INVINISBLE?