A foreign joke chocolate waterfall

In a science class, the science teacher said, "Niagara Falls is the largest waterfall in the world." At this time, the teacher found Xiao Ming sleeping, so he went up to him and said, "Xiao Ming, why are you sleeping?" Xiao Ming said, "I didn't sleep." "Then tell me what you just said, and you repeat it." Xiao Ming said, "You just said that your big rag is the largest rag in the world."