In pictures: US candidates' body language

However, Ms Wood says former Massachusetts governor Mr Romney suffers from a "nose-growing Pinocchio lying cue".

The expert - who has taught interview techniques to police - says there is something suspicious about someone making an affirmative statement, such as "I am innocent", while shaking their head.

She adds: "Romney does this all the time, making positive statements, such as 'The American people are the greatest in the world', but then shaking his head 'No'."