Why is one person immediately attracted to another?

United States
@trruk1 (1031)
December 6, 2009 12:03pm CST
This is a puzzle. Sometimes you meet someone and that other person is good-looking and clean and nice and--well--it was nice meeting them. Other times it is like sparks are flying. The attraction is so powerful it is almost visible. Sometimes you can sense it coming the other way, too. Why? The other person was just as nice but left you cold. This one sets you on fire.