Animal hearing has long served as a model for understanding human hearing. Yet conversely, animal hearing can only be imagined through human hearing. This chapter shows how, building on techniques for testing human hearing, experimental psychologists in the 1930s and 1940s turned to determining the absolute (upper) frequencies of hearing for various other mammal subjects. Showing the domains of animal auditory perception to be overlapping but rarely congruous with that of humans, these measurements began to lead lives of their own in the subsequent decades. Propelled by various scientific, military, and commercial interests, fascination with the ultrasonic stirred imaginaries of sonic control. The threshold of hearing, this chapter argues, is also a threshold to the imagination, as expressed in the simultaneous success and failure of mundane technologies such as the “Ultrasonic Pied Piper” or the “Bird-E-Vict.”