A dog’s sense of smell is many times more sensitive than ours, but why do they have to get so close to smell each other’s bottoms? Couldn't they pick up the scent from far away?
Do dogs who sniff each other bottoms fight or is bottom sniffing a kind of sign of peace between them? A sign of affection maybe?
Don't they sniff their masters' crotch as well - it couldn't be for identification. This behaviour must have another purpose for sure.
Do dogs have scent glands around their noses? If so this would be one way of putting their own scent on the other animal. BTW my ferrets also do it.


Dog’s anal glands emit scents that provide information about health, gender, and mood. Similarly, the genital area in humans also possesses a large number of scent glands which is why dogs sniff it as a way of getting to know someone unfamiliar.

That said, why dogs get up so close to sniff when their sense of smell is so acute implies it is not to catch some elusive scent, rather it’s a behavioural response as part of social interaction that will have evolved over hundreds of millennia if not longer. As an example, greeting another dog face-to-face could be dangerous if the other animal is hostile.