You’re taking your dog for a walk, perhaps down a verdant trail through the forest, or maybe along the beach, when your dog starts sniffing the ground with a bit more “focus” than is usual. He then starts acting as though he’s sniffed out the most delicious, intoxicating scent and is no longer responding to your calls, his name, or pulls on the leash. All of a sudden, he’s writhing on the ground, as though he’s having some kind of trance-induced fit in paroxysms of what could only be called pure and utter ecstasy, to anyone looking on.
At first it’s kind of alarming, and then becomes quite amusing, until… you realize just what is causing his frenzied rapture. When you get a glimpse (or a whiff) of the dead [bird, fish, mouse, squirrel] or other fill-in-the-deceased-animal here or slimy sea-goo, bird- or dog-poo, or other foul and naturally sticky substance, you start freaking out in alarm and sheer disgust.
So why on earth do dogs enjoy rolling in putrid smelling filth? Scientists don’t know for sure why dogs have this particular instinct, but one thing is certain: it is an instinct, and it’s not unique to your dog. As for what’s behind the instinct, there are a few theories:
The most popular theory is that it’s a holdover from their wolf ancestors: dogs roll around in smelly (to us: the most disgusting) things to camouflage their own natural odor. Masking their scent would have helped wolves sneak up on prey, enabling them to be more effective hunters.
Another idea is that dogs cover themselves in odoriferous substances to signal to other dogs that they’ve found something interesting. As you know, dogs sniff each other not only to “say hello” but to gain information about each other. Thus, your dog will be communicating: “Exciting news! There’s something deliciously dead nearby!”
Still another idea is that dogs have a primal instinct to thoroughly roll on dead things from their past as hunters: scent-marking the scent-maker (the dead animal) is a good way to publicly claim that carcass and keep any other scavengers away. Even though a bowl of organic, gourmet dog food may be waiting for him at home, he isn’t going to pass up the opportunity to signal “this is mine!”