Posttraumatic vocal disarticulation

Post-traumatic vocal disarticulation is a Human condition involving the vocal chords of a human being. After a period of extreme stress or trauma, a person diagnosed with this "disease" is rendered completely unable to speak, even if there is no catastrophic injury to their actual vocal chords. It is unclear if this condition is physical, or if it is merely psychological. However, the words post-traumatic may point to it being psychological, as Lucy was one of the two other surviving Spartan-IIIs in her company. The other 298 were all killed in a huge explosion.

Spartan-B091 Lucy is the only known case of someone being diagnosed with it in the Halo universe.