I believe it goes "When you're smiling, the whole world smiles with you"...
In LM's case, the whole world keeps smiling at you waiting for a smile back. Oh sure, we've cooed over the sleep smile and sleep giggle. We've gotten the half smile when we rub his cheek. We've even gotten what I classify as a "happy face"...but the elusive social smile still has yet to make its appearance.
We're close...so close. When TH comes home from work (after being home with us for weeks), LM is visibly happy to see him....but no smile. I know at seven weeks, it's perfectly okay to not see it yet and that it's coming. But, man! I can't wait.
Of course, I'm sure that LM will share this milestone in an unconventional manner...my money's on our furbaby getting rewarded with it when he licks his hand.