As humans, we have some societal restrictions (to say the least) with exposing our rears to other people, both new friends and old. For us, it is better to shake hands with new people and reaffirming bonds does not include asking your friends to scratch your rear. But if you were an animal, you would see things differently.
We know that cats are tuned into certain smells and their environment gives them much more information in scents than ours does for us. She is not trying to be offensive by walking up to you and placing her butt in your face. She is doing what is natural to her and allowing you to gain information about her. Because of her anatomy and her ability to learn from olfactory (scent based) clues, she is very comfortable with presenting her rear to you and assumes that you are comfortable too. She trusts you or she would not show you her vulnerable back side so easily.
For cats, rubbing is a sign of affection as well. They are able to release pheromones that label you as safe when they rub on you and as they rub, they just naturally also present you with their back half.
Cats are also very commonly affected by fleas and often suffer from a flea allergy. Flea saliva is one of the most irritating substances on the planet and a single bite can set off a violently itchy reaction in some cats, so even indoor cats that get a single flea bite from a flea that snuck in can be itchy. The irritation seems to localize to an area vets call the “tail head” which is the space on the back end right above the tail. If your cat is itchy, this is a really good spot for a scratch and she knows that you are a willing participant in scratching the itch!
Even if your cat does not have fleas or flea allergy, cats seem to like being scratched, rubbed or petted in this tail head area. So if your cat puts her butt right in your face, don’t be offended. Just know that she is treating y0u like she would want to be treated. She is merely following the Golden Rule!
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