Not sure how common this is but with a fair amount of the females i have fucked i have observed that they either subtly, or not so subtly enjoyed rubbing and fingering their assholes. For instance i had one female partner who, while in mish or in cowgirl always had a hand on her butt...she would deny doing anything when i asked what she was doing. I could feel her hand moving beneath her in mish while i fucked her pussy. Some of the subtle "ass teasers" would eventually admit it and show me what they were doing when they realized i was cool with it....there is something about having a chick look you right in the eyes while she lays back and has a couple fingers a few inches deep inside her asshole. I have even had a few not so subtle ass fingering moments...i was fucking a chick in college once and after fucking her a few times for a few weeks she started really opening up. I was fucking her on the floor in doggy in a well lit room one day and i saw her suck on a finger and reach back and push it inside her asshole...20 seconds later after seeing her put a second finger in and asking me to smack her sss i blew an intense load inside her pussy.
Anyhow...is this a somewhat common act for woman to do that men do not always catch onto or know is happening when they are fucking?