During orgasm, a human male experiences rapid, rhythmic contractions of the anal sphincter, the prostate, and the muscles of the penis. The sperm are transmitted up the vas deferens from the testicles, into the prostate gland as well as through the seminal vesicles to produce what is known as semen. The prostate produces a secretion that forms one of the components of ejaculate. Contraction of the sphincter and prostate force stored semen to be expelled through the penis's urethral opening. The process takes from three to ten seconds, and produces a warm and highly pleasurable feeling.
As a man nears orgasm during stimulation of the penis, he feels an intense and highly pleasurable pulsating sensation of neuromuscular euphoria. These pulses begin with a throb of the anal sphincter and travel to the tip of the penis. They eventually increase in speed and intensity as the orgasm approaches, until a final "plateau" of pleasure sustained for several seconds, the orgasm.
During orgasm, semen is usually ejaculated and may continue to be ejaculated for a few seconds after the euphoric sensation gradually tapers off. It is believed that the exact feeling of "orgasm" varies from one man to another,[31] but most male human beings agree that it is highly pleasurable.
from wikipedia
still trying to find out what exactly causes the pleasure :-/
btw even wikipedia states that autofellatio is possible (although it's for the other thread)
well other than the scientific explanation on why orgasms feel good, i have a theory that i came up with just now..
well as you all know, without sex the human race will go extinct(stating the obvious), so assuming that orgasms don't feel good, humans' wont really bother to have sex, because what's the point the future generation doesn't concern me.. unless you have an ego of a massive giant ball..
so feeling good from orgasms is an added incentive that will lead males to want to hump any living thing..
i got a theory (i read it in some book but i forgot)
when men ejaculate they release some kin of horon/secretion that give the feeling of ecstasy (feeling of aftersex)
errr.... i forgot about the hormon/secretion name and i also forgot about the explanation (too lazy too read the book again)