For the longest time, Scarlett did not laugh. She would smile big, and you could tell she wanted to laugh, but no sound came out. We discussed this with all kinds of doctors, audiologists, and therapists. I don't know if it is related to her hearing or just a quirk about her, but she still doesn't laugh much. However, that doesn't mean she can't.
I am pretty convinced that she is just a discerning critic, and we are not as funny as we think we are.