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.
[57] Success! Took My First Fist Tonight! Told My BF to Take a Pic. Hurt a Bit When His Knuckles Went In, but Felt Much Better with His Whole Hand Inside. My Hole Feels Sore Now but Very Satisfied.