You are preparing yourself for a scene, and the most important thing is to remain emotionally available and remain in the moment with your scene partner. You don't want to let your own self-consciousness block the flow of creativity that's coming out so that you can act and react, and play what the scene is all about.
Every batch of sperm represents an opportunity for genetic typos - called de novo mutations - to be passed on. A 20-year-old man and woman will each pass on about 20 de novo mutations to a baby they conceive. By the time the couple is 40, a woman's total has remained at 20, while a man's has jumped to 65 - and it keeps climbing from there.