Miles, our pug puppy, was 5 months old and mounting everything he could wrap his front paws around. “We’re having him fixed soon,” my partner and I repeated like a mantra to friends as they politely extricated their legs. This is how we found out about Neuticles.

Neuticles, one plugged-in acquaintance revealed, are prosthetic testicles for neutered pets. Kim Kardashian West’s boxer was Neuticled, as were Larry Flynt’s Doberman pinschers. Altogether over 500,000 animals have been surgically implanted with the silicone testes, according to Gregg A. Miller, who invented them in 1995.

“Some people throw the dog in the car and have him turned into a eunuch because they don’t care,” Mr. Miller said recently. “But there’s a certain segment of pet owners that do care, and that’s where Neuticles come in. And it’s not only canines and felines. We’ve done an elephant, we’ve done prairie dogs. I Neuticled a monkey in Pocahontas, Ark., and a colony of rats for the University of Louisiana.”

But the majority of his clients, Mr. Miller said, are “everyday pet owners who opt for Neuticles so their pet will maintain its dignity and self-esteem.”