Whenever I am in a position where a woman and I have or are deciding to be physically intimate with each other, I always like to make it a part of our relationship to talk warmly, openly and frankly about what they like, how they like it, talk about what lights their romantic and sexual fuse, what turns them off -- and I try to have fun while we're doing it so that they don't feel uncomfortable ever telling me what they want and how. I realized when I was dating after being divorced while in the USAF that the key to a woman's heart, soul and head was through her brain -- not her vagina. More often than not, I discovered that a partner would generally open up and tell me her deepest, darkest emotional and physical desires while having fun like this and talking, not rushing toward bed -- though there were times that I never got as far as I wanted to in discovering how she was wired when I was rushed and didn't always make it into bed.
If they ask me the same, I'll give them frank, honest answers and judge their response by watching their eyes, mouth and face. If I hit a nerve with them or get a generally negative response, I might turn it into a joke or a story. When I saw that one girl I dated in college didn't respond well to me mentioning that my anus was very responsive to touch, I told her that it was the result of falling off a ledge on a pogo stick as a child and that I had to bounce all the way home without my hands or feet ever touching anything on the trip (that got her laughing). On the other hand, I might indirectly use imagery to have her visualize things like that which might suggest to her what I like (especially if she hasn't directly asked me).
I usually accept my partners for who they are, try to feed their brains, emotional and physical needs and don't feel compelled to push any particular agenda of mine: after all, who knows better how to please me than me? It is always best when my hottest desires are met and shared by the love of my life, but I don't feel that I need to share it unless we broach the subject before, after and sometimes during sex.
If nothing is said by her for or against anal/rectal stimulation in advance and I have had several hours of long kisses and slow, delicious and delirious foreplay with her, I will watch her response to my every touch. Often, to help her relax and pull her back away from orgasm during foreplay, I'll often give slow body massages that can last more than an hour. I'll note how she responds to my thumbs pulling her buttocks apart to see if she tenses up or withdraws. Later, when I'm making my way toward her clitoris and bum with my mouth and tongue, I'll gain a firm grasp of her buttocks with both hands and measure her response. When I first start oral stimulation of her clit and vagina, I might detour slightly with the tip of my tongue and slowly circle her anus to again gauge how she reacts. I make particular note of how she touches me, both during foreplay and intercourse.
Sex to me is as much about meeting my partners needs, emotions and physical desires as it is about pleasing her. So this isn't about making a catalog of her physical responses, but more like us both writing our living encyclopedia of each other.
If I don't have a very good about what she physically responds to by the end of our foreplay, after she has had two or three orgasms, I'll try to get her to talk further about her desires while being playful. Where I have doubts or questions, I'll kid around with her and ask hot, leading questions. I'll also playfully suggest questions that she has to answer in very specific terms of creating visual images and ask her to guide me to each point when she tells me her answers.
But I always return to asking her questions about what turns her on if I feel that she hasn't had the chance or given herself the freedom to be completely honest with me. I'll ask her if she's ever had an enema, and whatever the answer, I don't feel the need to bring it up and discuss it then. But I might some time in the future write a hot story about her, mentioning those things that do turn her on, and I might add that "I had a dream about you..., and you were playing with my butt" -- or "In my dream, you were a nurse and you rolled this cart into my hospital room carrying a nozzle, tubing, a gallon of hot, soapy water that you had prepared and..." and suggest to her that she knew as my nurse that I secretly liked enemas. This could backfire on me, of course, but I would know in advance what kind of answer I might get. And just such a question has solicited interest in my desires.