. . . is that it's often difficult to determine when, exactly, a baby has done something for the first time.
For example, a newborn baby will often "smile" when a bubble of gas is making its way through. This can happen when they're awake, but it can also happen while they are asleep. It continues to happen while asleep for months thereafter. The theory is that babies do these gassy smiles, get positive reactions and social smiles from the adults around them, and decide to smile socially in order to get that reaction. But their efforts in this regard develop over the space of several weeks, so it can be very hard to determine which upturning of the lips was actually the first social smile, and which ones were proto-smiles.
Today's example: we're pretty sure we've had a few proto-laughs from Claire; that is, she made sounds that could have been giggles while smiling. This morning, she did it consistently four times in a row, in response to something vaguely funny in a baby way - Daddy beeping her nose. So is this the first verifiable giggle, or do we wait until the sounds get more giggle-like to dig out the baby book?
First words are similar. Many babies will say things by nine or ten months that are proto-words and have definable meanings for them, but their parents don't recognize it because the same sound can mean several different things to their baby - not because they can't distinguish between objects but because their vocal apparatii are not sufficiently developed to form the ends of words. Thus "Baa" refers to both the lamb toy (that is constantly being shaken in their face while mommy makes the noise that lambs make) or the bottle, or possibly their blanket. They know which one they mean. It's when the parent figures it out and establishes its consistency that the baby book is dug out and the blank for first word is filled in.
If I were writing one of those ubiquitous "baby firsts" books, I'd provide more than one space for things like early words and smiles, because the decision about which one is the first is so arbitrary that it's nice to record more than just one. On the other hand, considering how many people leave their baby-books half empty due to hectic lives and the decision to "do it later," it's really not that useful to speculate on what I'd put in one. I like livejournal for recording my baby's firsts and attempts at firsts.
So, today's first or really good attempt at a first: a real laugh, in response to having her nose beeped by a smiling Daddy.