A closer look
Long before silent dog whistles were a training tool, they were a gentleman's weapon of choice for annoying apex predators in the name of acoustic science. In the late 1800s, Francis Galton wanted to test the upper limits of hearing. So, he invented a tiny brass whistle capable of producing ultrasonic frequencies well beyond human perception, hid it inside his walking stick, and rigged it to a squeeze-bulb. Then, he casually strolled through the London Zoo, stealthily squeezing his cane to blast pure, silent torture at the enclosures. He meticulously noted which animals reacted (small dogs and cats hated it, lions mostly ignored him). He basically invented the modern dog whistle solely to serve as a high-society acoustic troll.
