Thinking about what you want to do for a moment, you hit upon a rather appropriate way to punish Emily for her secret vice. You follow her into the bathroom, and as she's changing into a fresh pair of panties you lay down your command.
~From now on, you will have a growing, uncontrollable compulsion to play with yourself constantly. It will start so weak you won't even notice, but as the urge gets stronger at least one of your hands will begin playing with your body when you aren't paying attention to what it is doing, with the other hand joining in when it isn't otherwise occupied. During this stage, you won't notice that you're playing with yourself unless either someone points it out to you, you see yourself doing it, or you are just about to cum. Eventually, you will be completely unable to control yourself, and be fully aware of what your hands are doing but powerless to stop playing, at most only being able to use one hand for brief tasks if necessary. You will not connect this issue to me in any way, but will accept any explanation I give you for why this is happening.~
You wait for Emily to finish changing her panties, then tell her, ~You will not notice your bedroom door opening and closing when I leave, and once I do, your awareness of me will return to normal. You will also want to let me in your room when I ask.~ You then swiftly make your way back outside her room and shut the door.
After a couple of seconds, you knock on the door again, "Emily, it's Eric. Can I come in?"
"Sure," you hear her voice say, and you walk inside. Emily is sitting on her bed with another book, apparently just about to start reading again.
"So, what have you been up to in here?" you ask, in an attempt to kill time until your command kicks in.
"Not a whole lot. Reading, for the most part." Emily says, doing her best to remain vague. You notice her free hand twitch slightly at this.
"Yeah, I noticed you have a whole bunch of engineering books in here," you say, "Is that something you want to do when you get older?"
"Probably," Emily replies, her fingers drifting up onto her leg, "Either that or be an architect."
"Cool," you say, though not necessarily at what Emily said so much as what you see her ready to do, "What else do you like?"
Emily tells you something about one of the bands on her wall, but you're only half-listening. After all, your attention is focused elsewhere. You manage to keep the small talk going for a couple more minutes, until the moment you've been waiting for finally arrives. Emily's right hand pushes the bottom of her shirt up and begins caressing her breast, while her left hand starts trailing around her crotch, her thumb hooked in the waistband on her pants. And the best part is that Emily doesn't appear to notice a thing, still talking as if nothing odd was happening!
"Um, hello?" she asks, momentarily lifting her hand from her crotch to snap her fingers, "You're real quiet all of a sudden. What's up with you?"
The hand that has been playing with her breast for the past few minutes started to push her bra out of place with its fondling, while her other hand was quickly starting to drift back towards her crotch. Should you let her in on what she's doing?