Fantasizing about your mother in law

Sometimes when my 73 year old mother in law is visiting. I sneak off to my bedroom And fantasize about her. I've found by putting peanut butter on my balls and anus And the getting my scottish terrier (pixie) to lick it off, i can almost imagine it is my mother in law. Pixies tongue is so soft and warm. Is this normal ? Does anybody else fantasize about their mother in law ?