Jerking To 'Mommy'

My wife knows that I have fantasies about her mother. We both call her mother 'Mommy'.

My wife sometimes likes to watch me masturbate and tells me to 'Jerk for Mommy', 'Cum for Mommy', and then when I am on the verge of cumming she will tell me to 'Fuck Mommy'. Hearing her say those words will get me off with the biggest orgasm every time.