What is it about smiles that, at least to Americans, are so appealing? I was buying something at my local CVS and when I chanced to smile at the checkout clerk who smiled back at me with a 100 watt smile. There was no apparent flirting going on. And, while I am most certainly capable of flirting, am pretty fit, and do look a bit younger than my chronological age, I was also at least as old as her grandfather. She was just responding to...