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