Who Taught Him That?

So many sounds coming from The Dude.  I love how he tries to communicate with us with his squeals and giggles (and crying....but that's nothing new).  But more recently it is almost like he is experimenting with different sounds. 

I was videoing him recently trying to catch him as he was on all 4's rocking, (He is pretty close to taking his first "steps" as a crawler.) and I caught him making this sound:

And here is a video of him going from nearly comatose (jk) to up on all 4's....and back down to his belly.