"Was.. was that a wink?"
"What? No, I was just blinking."
"But it was with just one eye."
"Yeah, Ruby controls one eye and Sapphire controls the other. We use to put a lot of effort into blinking in tandem, but it's just not worth it. That's why we started wearing the glasses; to deal with these kinds of misunderstandings."

Well, that's my headcanon. If only because how funny that is.