You’d think cats who live together would recognize each other by sight, but that’s not always true. Since cats have peripheral vision designed to track prey, they don’t see well up close but their sense of smell makes up for it. The universal way how cats say hello, is the classic butt sniff. This holds true for cats who have lived together for years, introducing a new cat indoors or cats greeting each other outdoors.
Anal sacs located on either side of the anus are an olfactory smorgasbord offering cats a “Google search” of scent identification. Cats can also say hello, by head-butting or bonking which trigger the release of scent glands and reinforce their social bonds. Licking and grooming each other is a sure sign two cats have bonded and consider each other family. If a cat does that to us, it means they’ve accepted us as one of them. Seeing formerly feral Domino and Merlin groom each other lately is especially heartwarming.
In this photo, Merlin is sniffing Odin. Note how Odin is offering his butt to Merlin to smell. This butt display not only shows the behavior for saying hello and who are you? but also their bond. Odin is assuming the position a kitten would to their feline mom who would clean their butt. It’s the same reason a cat shows their butt to humans. They’re saying, “Hi, how are you, mom?”
They don’t expect a lick, but a nice pat on the rump will do.