In two of his Ryan series he mentioned erotuic tickling as a foreplay: The Patrio games - in the middle of a book there is a scene when Ryan is in bed with his pregnant wife and he tickles her tummy as she squirms. 2: Newest "Dragon and Bear" - Chet Nomuri is in bed with a Chineese secretary and he notices her hairy armpits and starts to play with that hair. That tickles her and she laughs.