Today I found perhaps the #1 question to inspire that first spark of cognitive dissonance in a Muslim. Though I wouldn't recommend asking it in person.
Do Muslims today bow toward and circumambulate the same black stone, that the pagan moon god worshipers bowed toward and circumambulated as their moon god idol, before Mohammed?The answer is an unequivocal and absolute "yes".
So where does that leave Islam, since there is no historical or archaeological evidence that Mecca ever even existed, before the pagan Arabs built it in 4th century AD?
http://www.islamchristianforum.com/index.php?board=12.0
