"Oh, They're so cute! Are they twins?"

I just have to laugh. For 7 years I've been asked this funny question. Why do people ask this? My girls are identical twins. When they were tiny infants in a double stroller with matching outfits, I was asked if they were twins. When they were 3 and wanted their hair cut the same I heard, "Are they twins?" Last week, we were shopping and the cashier asked this. Now really, they are the same height, have the same color hair, and their FRIENDS have a hard time telling them apart. "Are they twins?" I just nod and smile. Yes, they are twins.