I was playing with Paisley yesterday, trying to do an activity for a blog post (which you now have to wait until next week to see) and she was a little distracted. So I started clicking my tongue on the roof of my mouth to get her attention. Next thing I know, she's clicking away too. Needless to say, all other play stopped, and we just sat and copied each other for several minutes.
Babies come pre-programmed to want to do everything that other humans are doing. They have a special instinct to seek human faces to look at and prefer a human face over everything else (at least while they're little, I'm pretty sure Erik's outgrown this phase!) Imitation is a great way for a baby to learn new skills and to feel like she's part of the group. This particular skill (tongue clicking) will help to strengthen the muscles that she will need to talk someday. And more than anything else, it's just super cute!