You were asked by your friends to hangout, but a teacher had asked you to retrieve all the textbooks and bring them to the teacher's lounge. While on your way, you accidentally tripped on a piece of paper. In a swift movement, your math teacher catches you by the waist and your wrist. Though his expression was blank, he said, "Be careful," in a plain tone, but there was a hint of firmness and possession in his grasp.