Have a parrot, or other bird, carved and painted, with simple springs to
make the head turn and the mouth to open, mounted on a hollow shelf
against the wall.
Through its body, one leg, the hollow shelf, and thence through the
wall, into an adjoining apartment, where your confederate can overhear,
run a tube with a mouthpiece, to which the lips or a bellows can be
applied.
On pretty Polly being addressed, she will whistle, sing, scream at
command, and answer to sensible questions.