For the most part, babies learn incrementally, picking up new skills bit by bit through trial and error. For example, Grace has seemed to be on the verge of crawling for months, and is now at the point where she's got everything down except for actually moving forward.
Once in a while though, Grace seems to learn new things in giant leaps, as if they were downloaded directly into her brain like Keanu Reeves in The Matrix but if Keanu was a better actor. Last Monday was one of those days. From the moment Grace woke up, it was like she was a totally different person.