How does ventriloquism work? --- Josh, Elgin, S.C.
The basic idea behind ventriloquism is to make speech sounds without moving your lips. That is easy enough on some sounds, but sounds like "B" and "F" are problematic. So to handle them you substitute easy sounds for the hard sounds.
A good ventriloquist adds to that the ability to manage two personalities simultaneously and switch seamlessly between the two in an instant. Doing that in a believable and convincing way is probably more difficult than the speech part.
You can see both of these skills in action in this remarkable video, where a skilled ventriloquist named Ella Havell explains how to speak without moving your lips:
See also these tutorials: