squeakers are tuned to an ultrasonic range in the 24 - 28 KHz frequency, which is out of human hearing range, but still fun for your best furry friend. (moderndogmagazine.com)
As Santa and his sleigh approach, the sound of bells and his deep «ho, ho, ho» would get higher and higher (like when an ambulance siren whizzes by) and then become completely silent, because he would move beyond human hearing range. (sciencedaily.com)
squeaker is out of human hearing range, but still fun for your four - legged friend. (hear-doggy.com)