One of the great benefits of Z's daycare is that they teach the babies infant sign language. Lately Z has been signing (and saying, too) "all done" when she's finished eating; she also makes other signs but we aren't quite sure what they mean. Signing is a great way for infants to communicate before they're able to speak.
I just realized a little while ago that R and I have our own form of sign language. We have signs for: "Z is asleep," "be quiet," "turn up/down the TV volume," "look at that," "this diaper is dirty," "where is xyz?" and "can you get me a drink?" There are probably a couple more, too. I don't exactly know when we developed these signs, but I'm thinking they started to emerge at times when Z was asleep and we needed to be really quiet. I just got out of the shower and poked my head out of the bathroom door because I wanted to know what time Z had fallen asleep. I looked at R and he signed "be quiet" because Z was still settling down a bit. He then mouthed "10 minutes." You know you're good at communicating when you don't have to say anything to know what the other person is thinking.