Bullhorn is Elwin’s pet banshee. Elwin keeps him in the Healing Center at Foxfire. Bullhorn is described as looking like a demented ferret with purple and grey eyes. Banshees can sense when someone's life is in danger and will scream or sleep on those near death. It has been said that when a banshee lays near you, it is a much worse sign then it screaming. Bullhorn has laid on Sophie twice when she was near death after having an allergic reaction and also almost fading away.
Note: Bullhorn is (assumedly) accidentally called Bullseye on page 337 (hardcover) of Nightfall.