Pharyngeal reflex

The pharyngeal reflex or gag reflex is an automatic response to any object contacting the roof of the mouth, the back of the tongue, the area around the tonsils and the back of the throat. When something contacts these areas, the soft palate raises and the muscles of the pharynx contract in unison.
This naturally prevents any foreign object from accidentally entering the throat and possibly entering the airway, and assists with the closing of the airway during the normal act of swallowing. However, where surgical procedures involve inserting anything through the throat, the reflex can also prevent the passage of the instrument and trigger vomiting. As such, most such procedures have to be performed under at least local anesthesia to suppress the reflex. However, this puts the patient at risk after the procedure is over until the anesthetic wears off.
Although a large proportion of individuals do not possess a gag reflex, and people can be trained to suppress it (most notably, sword swallowers) or induce it (bulemics), the lack of a gag reflex can indicate a serious medical condition, such as damage to a nerve. 
Pharyngeal reflex at Wikipedia
Category:Physiology