Wenis masturbation is commonly known as (in most households) interlocking the wenises of the fingers on both of your hands together. (As apposed to your wenises with someone elses). Most human beings are infact wenial hermaphrodites, which allows them to easily partake in wenis masturbation, without the help of a third hand.
Sara enjoys wenis masturbation. Unfortunatly for Aaron he was unaware of this and ended up with "blue knuckles" for which the only cure was wenis masturbation.