why do dogs sniff eachother's butts?

To get acquainted

To get to know them and to determine their health status.

Thats how they know each other

Pretty sure they got some sort of scent glands back there...

They use to identify each other with

They can't shake hands.

It's the dogs doorbell.

Cause they don’t have hands. Nose and tongue is all they got. 🤣

because they can....same with when they lick themselves....because they can