Butt sniffing is a very natural, instinctive and basic way of cat-to-cat communication. Firstly, it is because cats have the most developed sense of smell; secondly, their anal glands have the most information (gender, estrus or not, health and diet, fear and emotions, territorial marking).

The main functions of this behavior are:

Hello, Collect information about each other

For cats who meet for the first time and whose smell is contaminated (such as going to the hospital), sniffing the butt can also get a lot of useful information more accurately:

Quickly determine who I am and Have you met him or her before?

Is he/she nervous or aggressive? Is he/she a friend or enemy?

Is he/she in good health? Is he/she able to deal with it?

...

Dominant cats establish dominance and determine superiors and subordinates

Dominant cats usually take the initiative and sniff out the butts of other cats. When sniffed, they will make a hissing warning sound to avoid Being sniffed;

The weak cat will sit down and use its tail to resist the anus to limit its smell, disguise itself as air, and avoid being stared at by the stronger big brother.

Sending a mating message

If unneutered cats sniff each other's butts when they meet... the most important thing is to confirm each other's gender, whether they are in estrus, and to send mating information to each other.

A certain degree of consolation effect

When there are environmental changes or other environmental stimuli, sniffing (perianal and facial) between members of a stable relationship in a multi-cat family can help to a certain extent. Cats relieve tension and stress.

If a cat lets me smell its butt...

The cat exposing its butt to you means that it has no disguise in front of you and does not need to cover up its smell, even I am willing to share with you his diet, health status, emotions...all kinds of trivial matters.

For cats who are sensitive and suspicious by nature, this action fully expresses their trust and recognition of you!

What should I do if my cat lets me sniff it?

Behaviorists do not recommend interrupting this behavior (letting you sniff/cats sniff each other). This is the equivalent of stopping you from shaking hands with your friends for no reason - it's upsetting to people (and cats).