You might think of smell as a sense, but it's more than that—it's a chemical sense. That means that when you smell something, your brain gets information about what it is by receiving signals from the nose that are caused by chemicals in the air. You've probably already noticed how this works! When you walk into an old house and smell mothballs or see someone with a terrible foot odour, those smells are caused by chemical reactions between airborne chemicals and receptors in your nose. And since we can't see or hear these odours, they're invisible to us—but not to other animals! • For example: if you've ever smelled smoke from burning wood before hearing any crackling noises (which means the fire has gotten out of hand), then you know too well how important it is for us humans to have this second layer of protection against danger when our eyesight fails us—especially during times like earthquakes or forest fires where people may need help getting out alive from situations where even their best-intentioned neighbours might not be able to see them enough through thick smoke clouds. • But smells aren't only there for survival purposes either! They also make food taste better (and help prevent spoilage) by signalling hunger pangs within our bodies via hormones such as leptin which tell us when we're hungry enough that eating would be beneficial at this moment."