Your Ass and You

[Mudhammam]

The anal stage, in Freudian psychology, is the period of human development occurring at about one to three years of age. Around this age, the child begins to toilet train, which brings about the child's fascination in the erogenous zone of the anus. The erogenous zone is focused on the bowel and bladder control. Therefore, Freud believed that the libido was mainly focused on controlling the bladder and bowel movements. The anal stage coincides with the start of the child’s ability to control their anal sphincter, and therefore their ability to pass or withhold feces at will. If the children during this stage can overcome the conflict it will result in a sense of accomplishment and independence.

http://en.m.wikipedia.org/wiki/Anal_stage

So, I guess the anus is both a source of bliss and revulsion. It's like a metaphor for life.