ventriloquial

Her voice came, muffled, as if from the back of the top of his head. The ventriloquial effect was startling.

He threw half-crowns up into the air until they disappeared into the central blue, and then held a ventriloquial conversation, not in the best of taste, with the celestial spirits, who having caught the coins announced their intention of sticking to them.

We tried this a couple of times with no luck whatsoever, partly because whipbirds are notoriously ventriloquial and we could never agree on where the call was coming from.