The Annunciation here depends upon the medieval tradition concerning the unicorn (see Mary's lap) as a symbol of Christ. For more about this symbolism and why it would especially be associated with the Annunciation, read "The Unicorn and the Virgin" from the University of Dayton's Marian Institute.
We rightly admire Muslim neighbors and co-workers who put everything on hold five times a day in answer to the "call to prayer." But Christians have a call to prayer, too! It is the Angelus. Morning, noon and evening we are invited to pause and reaffirm our faith in the Incarnation: The Word was made flesh and dwelt among us (Jn. 1:14), because "God so loved the world that he sent his only Son" (Jn. 3:16).