Also in this movie, when he first visits Susan Sarandons characters house, and she plays the piano for him, as she is really getting into it and feeling it, Jack Nicholson says "Let it tickle you!"
I agree. I saw that scene and it looked to me like Jack tickled her feet. But it's not completely clear. Maybe it's in the book.
There're other tickle references in that movie. Cher tickled Susan Sarandon's side during the martini scene. Sarandon also says tickle quite a few times in the movie.