intertesting.... I have not noticed it with any of my pups, but I do know Cheli is ALWAYS sniffing Banks' butt when we are in the yard. Not so much in the house, but when outside, he seems to not be able to stop himself from going in for a sniff or lick.
edit to add... found this on the web
Powerful Sense of Smell
Humans can’t completely understand all the information a dog gets from smelling another dog’s butt. At least 33 percent of a dog’s brain is designed to process smells, as opposed to about 5 percent of a human’s brain. A dog’s sense of smell is so powerful that he can tell, for example, whether the dog before him in the veterinarian’s examination room was afraid, just by the smell the previous dog left behind.
They Can't Shake Hands
Dogs sniff butts to greet each other, much as humans do by shaking hands. Dogs have anal glands just inside their rectums, which produce a strong odor. Dogs can find out all sorts of information just by getting a whiff back there. They can find out the sex of the other dog, whether the dog is in heat, what the dog ate lately and whether the encounter is likely to be a friendly one. Because the smell is unique to each dog, butt sniffing is the best way dogs have to identify each other.
It Calms and Grounds Them
When a dog already knows about the other dog from a prior sniffing, he still smells the other dog every time they meet. Two dogs who live together typically smell each other’s butts when they come in from outside. So butt sniffing has another purpose: it’s also a dog calming mechanism, according to Kevin Behan, a Vermont dog trainer and author. Anytime something new happens—especially something stressful—dogs tend to sniff each other’s behinds. It satisfies the urge to do something, and it grounds them.
Dogs Might Get into Trouble
Some dogs, when meeting another dog for the first time, are enthusiastic sniffers. But the dog being sniffed might not take too kindly to all that focused attention. Whenever your dog is meeting another dog, be attentive. If the butt smelling is an unwelcome gesture, it’s time to separate the dogs.