Humans actually have four nostrils — two exterior nostrils, or nares, and two internal nostrils, called choanae, which are part of the posterior nasal aperture. Choanae connect the nose to the throat and help with breathing. Rarely, humans or animals can be born with choanal atresia, or blocked choanae, and require surgery to be able to breathe properly.

More facts about nostrils and choanae: