A: I have to go back upstairs. B: Why? We're already late. A: I have to check the stove. B: What's the matter? A: Maybe I left the burner on. B: No, you didn't. I checked the stove before we left. A: Are you sure? B: Of course I'm sure. A: Well, I have to go back upstairs anyway. B: It's getting later every minute. A: I think I left the water running. B: No, you didn't. Let's go! The only thing running is the clock!