Obligate nasal breathing describes a physiological necessity to breathe through the nose (or other forms of external nares, depending on the species) as opposed to breathing through the mouth. Definition The term may be misleading, as it implies that the organism has no choice but to breathe through its nose; however, it is also used to describe cases where effective breathing through the mouth is possible but not preferred. Alternatively, the term has been defined by some as the ability to breathe through the nose while swallowing. While this ability is a common trait of obligate nasal breathers, clearly this definition does not require that nasal breathing in any way be obligatory to the animal. Even in obligate nasal breathers such as horses, rabbits, and rodents, there is a potentially patent path for air to travel from the mouth to the lungs which can be used for endotracheal intubation. It has been suggested that obligate nasal breathing is an adaptation especially useful in prey species, as it allows an animal to feed while preserving their ability to detect predators by scent. Animals Horses are considered obligate nasal breathers. The respiratory system of the horse prevents horses from breathing orally. The epiglottis rests above the soft palate while the animal is not swallowing, forming an airtight seal. Oral breathing can only occur with significant anatomical abnormalities or pathological conditions. For example, denervation of the pharyngeal branch of the vagus nerve results in dorsal displacement of the soft palate (DDSP), and it has been suggested that this leads to a clinical syndrome which may include oral breathing. However, significant respiratory dysfunction including airway obstruction is observed with DDSP, and the animal cannot function normally in this state. Rabbits, cats, and rodents are also obligate nasal breathers. Like horses, the normal anatomical position of the epiglottis causes it to be engaged over the caudal rim of the soft palate, sealing the oral pharynx from the lower airways. Air entering the mouth will not fully make it to the lungs. Even so, rabbits with advanced upper airway disease will attempt to breathe through their mouths. Many other mammals, such as dogs and adult humans, have the ability to breathe indefinitely through either the oral or nasal cavity. Humans According to Jason Turowski, MD of the Cleveland Clinic, "we are designed to breathe through our noses from birth — it’s the way humans have evolved."