My Mind is a Gutter

I was working with a long-time client and while I was working on his forearm he casually mentioned that he used to have a really big muscle "right here" and then he touched his pronator teres.  (This muscle pronates or turns and flexes the forearm.)  Client asked me if I had any idea how a young man would get such a big muscle there... and my mind went to the gutter. I tell him that I have an idea but I would rather not say. Client looks at me confused and tells me to say what I am thinking. Sheepishly I say "Self love?".  My client starts cracking up and says "MILKING COWS!"  Oops!