ANSWER I : Ventriloquism is the art of projecting or `throwing,' the voice so that is appears to come from a different source. The performer also directs the attention of the audience to the place from where the sound is supposed to come. The sounds are produced in the usual method adopted in talking, but the lips are held as nearly and motionless. Sounds are modified by the throat and palate. Consonants are often changed to avoid lip-moving syllables. Lack of facial expression on the part of the performer helps to fool the audience.
ANSWER II : Ventriloquism relies on the fact that the ability of the human ear to locate the source of a sound without visual and other cues is very poor. What the ventriloquist does is to supply misleading cues through the use of what we `masters of deceit' refer to as stagecraft and voice. Stagecraft consists of using gestures, eye movements, patter, and so on to direct attention to wherever the voice is supposed to be coming from. Ventriloquism is the ability, not only to talk without moving your lips but also to alter the pitch and cadence of your voice so as to create a second personality, which you can then bestow on the object of your choice. Scientists have explained the trick of ventriloquist in detail, and have managed to produce the reverse effect — where people are tricked into believing their ears over their eyes. People place different amounts of faith in their different senses. This is exploited by ventriloquists, who fool us into thinking sound is coming from someplace it isn't by relying on the fact that people use their vision more heavily than their hearing to locate the source of a sound. This is because the eye's retina is very sensitive to the direction of light that hits it, while the ear isn't so sensitive to the direction of a noise.