She thinks she has to.

She slowly walks over to the puddle of come on your desk and brings her mouth close to it. She looks up at you. "Do I have to, John?"

"I'm afraid so, Ashley. I need someone working for me who can prove their dedication."

You watch as she slowly touches her tongue to the white glob. She slowly licks up the come, swallowing several times after each droplet. When she's finally done, she gives the tabletop around the spot a good shine, then stands up, shamefaced.

"Well, you've earned your raise, Ashley. You're excused for the rest of the day, but I expect to see you here again tomorrow."

"Yes, Master- I mean, yes, John," she says quietly, then turns and leaves.

A few minutes later, Doe taps on the door and you tell her to come in. "Ashley's leaving early for the day; is she having problems at school or something?"