Peek-a-boo

XYZ will have a biology test soon and she is a bit behind in lessons. So she asked her schoolmate for help and he promised to come over to learn together. But a lady is always a lady, and XYZ doesn't want to disappoint, so she checks herself in the mirror, not leaving out any details. This is the moment when her schoolmate steps into the room, and he decides to start to explain biology right from that point.