Billy's father was a chemist. He often took Billy to the lab on weekends. He let Billy do his own experiments. One day at the lab, Billy showed his dad a handful of pills. Billy said, "I made these last week. Guess what they do." Dad said, "Well, you hate taking showers. I guess they make your skin repel dirt." Billy laughed. He said, "No. These are fart pills. They make farts look like rainbows. You know how Grandpa's always blaming the dog? Well, now he won't be able to. Everyone will see where the fart is really coming from." Dad said, "That's funny. But do they really work?" Billy said, "Yes. I've been testing them. Watch!" He farted loudly. A rainbow of colors escaped rapidly from the seat of his pants. They both laughed. Dad said, "You've got to promise me one thing. Don't slip any to your mom!"