During normal speech, the soft palate muscle in the mouth moves up and down and touches the back of the throat. To produce oral consonants (letters such as p, w, and x), the soft palate closes against the back of the throat. When the muscle closes tightly against the back of the throat, air cannot come out the nose. Velopharyngeal insufficiency (VPI) is when the soft palate does not close tightly against the back of the throat, leading to air coming out the nose (characterized by hypernasality and/or nasal air emission) during speech. This can cause speech that is difficult to understand.