Stuttering affects the fluency of speech.  The onset of stuttering typically begins during childhood and in some cases lasts throughout life.  Stuttering can present itself in different forms such as repetitions of words or parts of words, prolongations of speech sounds, or completely stopping speech or “blocked”.  Interjections such as ‘um’ or ‘like’ can occur particularly when they contain repeated (“u- um- um”) or prolonged (“uuuum”) speech sounds.  Individuals who stutter will also use interjections intentionally to delay the initiation of a word the speaker expects to “get stuck on.” Individuals who stutter can also appear tense when talking or out of breath.

See more at: http://www.asha.org/public/speech/disorders/stuttering/#sthash.BCOryGFJ.dpuf