What Unique feature is use to Identify a Genuine Rolex Watch?

How can I know what to look for on a rolex to know if its real or fake.|||Search Yahoo answers - I saw someone else answer this, basically the second hand must rotate smoothly (not jerk once per second), and the gears must be blue (you have to open the case, there's no window). The sites below have more detail.|||I think the second hand will pulsate instead of tick or move smoothly. That is the difference someone told me before.