Error - be unique!

When people are attracted to each other, they tend to sit or stand in the same way and copy each other's physical gestures. This is known as 'mirroring'. When someone does this, it marks good communication and shows us that our interest is reciprocated. Mirroring also happens when talking to close friends as well as potential lovers, so be careful as you may misread signs of friendship as signs of love.
Source: http://www.bbc.co.uk/science/hottopics/love/flirting.shtml