Really, this was largely born out of curiosity and impulse, all of which made sense when she decided it. She's honestly interested in how long he can keep it up (and how long she can keep it up too, but there's also that pesky stubbornness factor, i.e. as long as he can do it, she can manage just a little longer).

Besides, these little surprise dominant moments are sort of fun for her.

She's starting to regret her order just a little (she hadn't realized how much she appreciates the little ways he has of urging her on, okay?) but she also is trying her damnedest to refuse to cave on it. His attempts to follow instructions are really pretty cute, and yeah, she's getting kind of aroused, but one thing at a time.