The Fox 40 Caul® has a traditional harmonized trill tone and clear loud sound The Cushioned Mouth Grip (CMG®) provides soft contact area and reduces impact on teeth Compact pealess design for flawless performance Flexible fingergrip fits various hand sizes and reduces transfer of impact energy to the hand Elastomer material is warmer in cold arenas Indestructible polycarbonate body No moving parts to freeze, jam or deteriorate Flawless, consistent and reliable The harder you blow, the louder the sound Easy to blow and cannot be overblown Will be heard above ambient noise Official whistle of the NHL