I did not know this:
Sharia's Sinister Smiles :: Raymond Ibrahim: The totalitarian nature of Sharia law can only be grasped when one appreciates how thoroughly it permeates and dictates everything in a believer's life—including when and to whom a Muslim may smile.
Popular Islamic TV preacher Sheikh Muhammad Hassan appears in this video clip asserting that, according to Sharia, it is "not at all permissible" for Muslims to smile at non-Muslims, "except in cases of da'wa."
Often translated as "missionary work," the word da'wa means to "call" or "summon" non-Muslims to Islam. Because it shares the same goals of jihad—empowering and spreading Islam—da'wa is often seen as jihad's nonviolent counterpart.