Milk, Moon, Pencil, Roller Coaster, Ruler, Sail Boat, Snakes. Find out about the inner workings and origins of the things that pique your curiosity. Milk: Milk is a liquid that comes from the mammary glands of mammals. Moon: The moon is a natural satellite, an astronomical object that circles around the planet earth. Pencil: A pencil is a writing or art instrument that contains a narrow, solid pigment at the core, enclosed in a protective casing. Roller Coaster: A roller coaster is an amusement ride that we usually see in theme parks. Ruler: A ruler is an instrument that is used to measure distances or draw straight lines. Sailboat: A sailboat is a watercraft that is driven by sails. Snacks: Snacks are portions of food that are usually smaller than meals and are eaten in between breakfast and lunch, lunch and dinner, or even late at night long after dinner.