Antifreeze is a liquid you mix into the water in a car's engine so that water cannot freeze into ice and crack the engine in cold weather. Most of it is a kind of alcohol (often ethylene glycol, sometimes a safer cousin). Though actually it does more than the name says. It also helps stop the water from boiling too easily in hot weather, and it protects the metal inside from rust, so drivers in warm places still use it. The water-and-antifreeze mix is what people mean by coolant. It often looks bright green, orange, or pink so you can see a leak. One messy truth: it can taste slightly sweet, and it is poisonous, especially to dogs and cats who might lick a spill. Wipe it up. You put it in the radiator or coolant tank, never in the petrol tank.