Ventriloquism - altering your voice to make it sounds like it's coming from somewhere else - is familiar to most as entertainment. Performers beguile audiences by making their voices seem like they belong to a dummy, chatting with their playful, inanimate partner.
Ventriloquism is not a modern art - it dates back to at least the classical Greece, when it really freaked people out. Back then, ventriloquists were called 'engastrimyths.' Basically, people believed engastrimyths had demons in their stomachs who belched words from their host's mouths.