system
Given the following post, respond as if you're commenting on Reddit:
human
How does someone "throw" their voice?
gpt
They shout "SUL MEY GUT"! ;)

In all seriousness though, a ventriloquist "throws his voice" using two techniques; 

1) The forming of all sounds has to be done with the lips slightly parted. This is especially hard for the labial sounds, f, v, p, b and m, and there is really no other option than to replace them with other sounds such as th, d, t and n. When done skillfully, it's hard to hear any difference. 

2) The puppet/dummy is used to divert the audiences attention from the ventriloquists face. Our eyes tend to be drawn to things that moves irregularly, so moving the puppet/dummy helps to solidify the illusion. 

A fact is also that most ventriloquism is performed with the audience a considerable distance away, and often using a PA system as well. This diminishes or eliminates the audiences sense of where the sound is coming from. When watching a ventriloquist up close, the sound can clearly be heard coming from the ventriloquists mouth.