Selective mutism is a psychological disorder that is characterized by the lack of speech in some social situations while in other situations speech remains unaffected. There are two hypotheses regarding the etiology of selective mutism. One hypothesis suggests that selective mutism is the result of increased anxiety and extreme shyness while the other hypothesis suggests that selective mutism may be the result of oppositional behavior. The purpose of this study was to increase the vocalizations in a selectively mute participant. The participant was six years old at the start of the treatment, which took place at the University of Iowa children's Hospital. The results showed that during post treatment Eliza had a higher vocalization rate with novel individuals than all other conditions tested. However, other explanations are also possible, including an increase in the amount of people in the room allowing for fewer opportunities to speak, may be also be possible.