In humans, the same primitive area of the brain stimulated by food or sex is also stimulated by acts of altruism. 人類大腦中受食物和性刺激的腦區也受利他主義行為的刺激。
The sex organs and the mouth are the two most easily stimulated erogenous zones of the body, and it is therefore only natural that they should be brought into direct contact. 性器官與口腔是身體的兩個最容易刺激的性敏感區，因而打開頭就應該讓它們直接接觸是再自然不過的事情了。