Hi, I am not video taping for dys for our dd3, but had some unexpected smart stuff caught on video a few times when I've brought out a book or puzzle that she loves and has lots to talk about - pictures of different animals, words she can read (I guess), details she can talk extemporaneously about, like why she thinks one kind of chicken is the boy and one is the girl.
So, like Kriston said, get a conversation rolling might be a better bet, probably will take a few tries and for you to just go with her flow...that part is hard
