Dogs, like humans have two nostrils. But, unlike humans, dogs can control each nostril! Dogs have special muslces that can control their nostrils. This is very useful for dogs because they are able to sense what direction a smell is coming from. They can close one of their nostrils and identify exactly where a smell is coming from! Dogs smell the world like we see it, so this adaptation is very important!! That is why dogs can control their nostrils independently!