Is it normal that i like to sniff my cats butt?

Every time I get a chance to smell her butt, I do. Afterwards I feel ashamed of myself for doing it, but I continue to do it every time. I don't like to touch or do anything to her butt.. just smell it.

For some reason it just always happens, like i'll be sitting on my couch, she'll come over onto the arm and ill just lean over and sniff her butt while she is looking off the arm or something..