If you train your slave properly, you can expect to see this kind of pride on it's face after an intense session of abuse because it's position in life is so thoroughly reinforced that it finds it's purpose in serving and accepting daily punishment.
When your cunt is serving you and your friends, it is a nice touch to attach a clit clamp with a bell so you know where she is at all times...this allows her to be found quickly if your guests need to use her....