The vaginal walls contain significantly fewer nerve endings than the clitoris and anus, and therefore intense sexual pleasure, including orgasm, from vaginal sexual stimulation is less likely to occur than from direct clitoral stimulation in the majority of women.
Intercrural sex among men who have sex with men (MSM) is sometimes known as the "Princeton First-Year", the "Oxford Style", the "Oxford rub", or the "Ivy League rub", and is a form of same-gender frottage, or colloquially "frot".
They may regard it as an enhancing element of their sex lives or as their primary form of sexual activity.
The internal and external sphincter muscles control the opening and closing of the anus; these muscles, which are sensitive membranes made up of many nerve endings, facilitate pleasure or pain during anal sex.
By contrast, each person's sphincter muscles react to penetration differently, the anal sphincters have tissues that are more prone to tearing, and the anus and rectum do not provide lubrication for sexual penetration like the vagina does.
Researchers say adequate application of a personal lubricant, relaxation, and communication between sexual partners are crucial to avoid pain or damage to the anus or rectum.