In The Exorcism of Emily Rose, for the explanation of voices in tape, the prosecutor says that humans have two vocal cords and Emily had activated the other one too, which made her sound like two voices coming together. Is this possible?
Apparently it is possible but takes years of training:
There is a vocal technique used by Tibetan monks which allows them to literally sing a chord, or three notes simultaneously. This technique is not considered appropriate for most styles of western popular music, and therefore is somewhat of a mystery to many in the west. The technique when properly done has a pronounced droning which sounds similar to a digital audio effect. The technique may take years to master, but can be mimicked by producing a low sound from the back of the throat, and then shaping the tongue against the roof of the mouth as if sounding out the letter R. Adjust the shape of the mouth slightly until you hear harmonic overtones which are two octaves higher than the note being sung.
Further ref: http://www.scena.org/lsm/sm2-9/sm2-9Nomads.html
I have sung in various choirs throughout my life and have never come across anyone who did this or any music scored for it so I am guessing it is very unusual.
It is likely to refer to the false vocal cords explained here:
The vocal folds ... sometimes called 'true vocal folds' to distinguish them from the false vocal folds. These are a pair of thick folds of mucous membrane that protect and sit slightly superior to the more delicate true folds. They have a minimal role in normal phonation, but are often used to produce deep sonorous tones in Tibetan chant and Tuvan throat singing, as well as in musical screaming and the death growl vocal style.
The false folds are also called vestibular folds and ventricular folds.
The vestibular fold (ventricular fold, superior or false vocal cord) is one of two thick folds of mucous membrane, each enclosing a narrow band of fibrous tissue, the ventricular ligament, which is attached in front to the angle of the thyroid cartilage immediately below the attachment of the epiglottis, and behind to the antero-lateral surface of the arytenoid cartilage, a short distance above the vocal process.
The lower border of this ligament, enclosed in mucous membrane, forms a free crescentic margin, which constitutes the upper boundary of the ventricle of the larynx.
The vestibular folds of the larynx play a greater role in keeping food and drink out of the airway, breathing, and phonation (speech). People who have had their epiglottis removed because of cancer do not choke any more than when it was present.
They have a minimal role in normal phonation, but are often used to produce deep sonorous tones in Tibetan chant and Tuvan throat singing, as well as in musical screaming and the death growl singing style used in various forms of metal.
They are lined with respiratory epithelium, while true vocal cords have stratified squamous epithelium.