Two stoners are sitting on a couch after just having smoked. They hear a knock on the door. A half hour passes. One of them says "I think someone knocked on the door." A half hour passes. The other says "Maybe we should see who it is." A half hour passes. They get up and walk to the door. A half hour passes. They open the door. On the other side is their friend, another stoner. He grins when he sees his friends and says "Damn, you two are quick!"