Is it normal to sniff my finger after I stick it in my girls ass?

I sometimes let my 8 year old brother put his finger in my butt and vagina when we are home alone but for some reason he likes my butt more. He always looks at my butt when I walk or when I'm on my bed. It turns me on when he looks at it. Like one night our mom and dad were not home and I was in front of the mirror bending over and spreading my butt open and I was looking at my butthole and my little brother saw me and he came in and went around and saw my butt and he looked in the middle and he was staring at my butthole and it turned me on that he was looking at it. And he puts his finger up my butt and he sniffd it and he said "your butthole stinks but in a good way it does not smell like poop it smells like butt and I love it"