I'm not sure what it is but all the dogs in my family love the Booda Hedgehog toys. Misha has two, a small one and a large one. When other dogs come over, I have to hide them. She'd be really mad if someone destroyed her hedgehogs! These are good quality stuffed animals. They are durable and can take a beating. They seem to hold up well to chewing. Their shape makes it a bit more difficult for dogs to tear them apart, though Misha's big hedgehog is missing its nose. These come with a squeaker or a grunt noise maker. The grunting seems to really get the dogs excited. For the price, I think these are about the best stuffed animals you can go with. They are long lasting and dogs love to play with them.