Not too much of a mystery here... my dog's tail is constantly up with his butt on full display, so it's easy to establish a safe proximity to give it a quick sniff to alleviate my fears that his butt will smell terrible (I haven't actually done this in months). To get a little more specific from my prior claims, his butt actually smells like literally nothing, and yes, I do mean "literally". Every other part of him has some kind of smell, especially his paws and face. Well, I've never put my face anywhere near his reproductive bits so I have no info there. I do, however, always give that area a quick wipe whenever we get in from a walk (he's a small dog).

Hopefully this isn't TMI and in the spirit of this article!

This really turns up the curiosity related to questioning what exactly dogs are smelling when they do this to each other.

They're smelling anal gland secretions, which are too subtle for humans to detect.

That might be what they're sniffing, but anal gland secretions are not subtle. They're the opposite of subtle.

I have a lot of dogs. Every once in a while, it seems that one of them gets a plugged up anal gland, or it doesn't get fully expressed when they poop. An earlier commenter said to look for liquid dropping out when they poop; I see this all the time. But sometimes that doesn't work for whatever reason, and then later on the gland "pops" and all the stuff comes out. The dog is usually sitting on my lap when this happens. It happens with both girl and boy dogs. My wife calls it getting butt-juiced.

The smell causes me to immediately change my clothes. It's not a fecal smell. I can't begin to describe it, but once you smell it you'll never forget.

Years ago we fostered a girl dachshund who loved my wife but hated me and feared me like the devil himself. Often when I would approach her in any but the slowest and most non-threatening way, she would tense violently and squirt anal gland juice like a skunk. Sometimes she'd leave a trail of the stuff on the floor as she ran for her life. One whiff would tell you it wasn't urine.

(BTW, that poor girl dog was eventually adopted by a sweet single woman and they are now inseperable companions)

This is true. I meant that they are subtle in the amount available when dogs butt-sniff each other. Dogs can detect the tiniest amount, way before a human even notices it's there. The concentrated stuff is, as you say, very intense.

Ah right, of course, that makes sense.

> The smell causes me to immediately change my clothes. It's not a fecal smell. I can't begin to describe it, but once you smell it you'll never forget.

I'm sorry to put this in your head but... fish sauce.

With really old dogs the gland sometimes won't unblock itself and becomes infected. The cure is to milk it. This is a vet's least favourite job, and they have some pretty grim tasks.

Source: I heard it from a vet.

> The mind boggles at how you've determined this...

Depending on pup, you can easily get a bunch of body parts shoved into smelling distance without any effort other than continuing to be alive. Then it's just a matter of recall and forming an opinion.

Dogs tend to be pretty physically close to humans. If your dog had stank-ass, you'd know it.