The 738 55 Rule

Only 7% of a message is based on the words while 38% comes from the tone of the voice and 55% from the speaker's body language and face. The highly analytical type, you know, the people that seem completely emotionally detached, when they think you're not looking, they reveal everything. You don't have to worry about the look on your face. If you're really interested, the more interested you look, the more they're going to talk.