Just a quick query. My 6 month old dd has laughed no more than half a dozen times, and I'm not sure if I should be worried. She smiles lots, and very often looks like she's laughing, but with no sound. We play with her lots, tickle her, play boo, all the usual laugh inducing stuff, and nothing works. Could there be a reason for this, or is it just something that will come with time? I'd appreciate any advice and experiences.