I've been waiting for the day to come when the girls would really interact and "play" with each other, and tonight, while I was preparing the girls' dinner and I had my back to them, I heard high-pitched giggles and laughing.
When I turned around to see what was going on, Caroline (on left) had started this game where she would grab Claire's arm and that would start Claire laughing, in turn causing Caroline to laugh. Up until today, Claire has been really smiling at Caroline and trying to get her to react, but Caroline usually just stares at her.
Finally, today, Caroline initiated the interaction and was laughing it up with Claire. Now I have to space them farther apart when they eat because they've started reaching out with food-covered hands while I'm trying to feed them. Just in the last week, they have started smiling at each other and laughing and really "noticing" each other without my having to prompt or show them. They've figured out that they have a built-in best friend, and how amazing to think that they will have shared every moment together from the very beginning!