Hear Doggy! toys give your pet the same sensation and enjoyment of traditional squeaky toys without the irritating noise. The science behind Hear Doggy!: Dogs can hear sounds at a higher frequency (0 to 45KHz) than humans (0 to 20 KHz). Tuned to an ultrasonic range in the 24-28 KHz frequency, each Hear Doggy! squeaker is out of human hearing range, but still fun for your four-legged friend. These sturdy characters are made with Chew Guard Technology™ a manufacturing process that adds a tough, durable liner to every toy. The reinforced seams and specially engineered lining were made to withstand the rigors of a dog's play. Dogs are tough but Chew Guard™ is tougher.