What jokes can make people lose several pieces at once?

Playing mobile phone in class today was invited to the office for coffee by the teacher. Say hello to the teacher as soon as you enter the door: Hello, Miss Zhao! Hello, Miss Li! "Why didn't you call me?" "Teacher, I don't know you?" Then I'll give you a hint, Koutian. "Hello, teacher!" Then don't go back to the dormitory until after school!