Before being a wife, she is a woman. Even if the man in front of her is a customer, her chest and vagina tingle involuntarily when faced with an erect male. Furthermore, doing such things might get her scolded… this sense of taboo only adds to it, making the wives' privates soaked and slippery. The sight of them being embraced by men other than their husbands, moaning and crying out in ecstasy, is nothing short of the embodiment of eroticism.
