Nothing in the picture moved but Old Pretty's tail and Tess's pink hands, the latter so gently as to be a rhythmic pulsation only, as if they were obeying a reflex stimulus, like a beating heart.
Irregular, rapid beating or pulsation of the heart.
Time the beam right and the star could be turned, in effect, into an FM transmitter-broadcasting to the universe on the underlying carrier-wave of the Cepheid's pulsation.
