The Moose Horn� is an open-reed style call that is 100% FREEZEPROOF. The Moose Horn� reproduces the mating call of an Estrus� cow. - Open-reed style is 100% FREEZEPROOF - Unique �hose in horn� design automatically reproduces the deep guttural moans of rutting cows in Estrus� - Includes instructional CD explaining how to reproduce Estrus� moans and how to use your voice to imitate the grunts of bulls - U.S. Patent No. 5910039