If ******** cow's milk is "unnatural," something's seriously fucking wrong. lol
As far as "natural" when it comes to anal sex, well, take your pick of entrances to your partner... The vagina is most obvious, but then there's the mouth and the ass as well....
People have been fucking each other in every single available orifice for aeons...it's perfectly natural, any way about it. People just need to get over their hang-ups and get out of Sunday School "Training Camp" once in awhile. lol