"Desire Me"

 
She can use this Wish Word to watch him do this when he is naked at home and she can even ask him to do this when out in public, eg at a restaurant.

As his Desire isn't touched he needs to get aroused just from thinking about sex, and it can be fun for both if she helps him achieve her request by engaging in some erotic talk.

If he is standing in front of her during Affirmation she can enjoy watching him grow. And if she helps him along with some erotic talk she can see how he responds to different topics - a fun way for her to find out what really turns him on.