Why do dogs have slits on the sides of the nose? Dogs breathe in through the nostrils and out through the slits on the nose. This allows them to always bring new air past their olfactory receptors – and they can breathe in and out at the same time. Dogs’ noses are truly remarkable: the average dog has a sense of smell 100,000 times better than the average human. A dog’s brain has a much larger area dedicated to the sense of smell than a human’s, and dogs generally have between 125 and 250 million smell receptors. The Bloodhound has 300 million smell receptors – and the average human a measly 5 million. Bloodhounds can smell things up to 40 feet underground, and smell if a human touched something several days – up to a week – earlier. Another interesting fact about dogs’ sense of smell is, they can smell separately with each nostril, and this helps them locate the source of an interesting scent. They also have a special scent-detecting organ – the vomeronasal organ – that helps them detect pheromones.