I think our boy sort of got a joke yesterday (!):
He was sitting in the car next to Mali. She said, "I'm 'A-a'." I said, "Nice to meet you, 'A-a'." She said, "nice to meet you!"
I then asked Leelo what his name was, and he imitated the entire "A-a" exchange. Surprising enough. Then he giggled and said, "Nooooo!", so I said, "Is "A-a" not really your name? What is your name?" He said, "My name is LEELO!" and started laughing. Wouldn't be entirely surprising for our cheerful, giggly boy to have a sense of humor.
Also, today he was using nodding and head-shaking for non-verbal yes's and no's while using the toilet. If it was a coincidence, it was eerie.
Feeling optimistic at the moment.