Pornography is not a unidirectional influence. People view porn that arouses them. However, the Wilson principle predicts that the interest in any sexual activity will wane as the consumption increases. So ... men (and women) watch porn they like, but the availability of porn can influence - what we like. I caution my (college) students about this - and the potential to become attracted to more dangerous versions of sexuality.
That said, anal sex is not far from the mainstream anymore. I he is viewing anal sex, then he has some interest in it. he may simply think you will judge him negatively for saying it.
People watch threesomes because they are interesting. However, fears (legitimate and otherwise) are the biggest factors keeping them from trying it.
Men view more visual porn than women. If the women in their lives really wanted to understand their man's interests, she would spend some time perusing his entire collection.
Men should spend time understanding their woman's sexual interests - or simple romantix interests.
Nobody should engage in sexual behavior they find repulsive, but both might try to keep an open mind and find things to do which better explore available possibilities.
With out this, sex WILL become rote and uninteresting. At that point the interest level in porn or (romance novels, etc.) goes way up. Porn as a replacement for a partner is not healthy. Porn as an exploratory device is.
By the way, we did research on why men enjoy certain porn. What emerged as the number one factor, even edging out physical attractiveness of the stars, was the degree to which they believed the star was 'into' what she was doing, and 'into' her male counterpart. Follow-up with the participants who volunteered to be interviewed, suggests that many men fantasize about being 'wanted' or 'craved' actively, rather than feeling like they were being 'serviced'.