Their body language may tell us as much as their words. Last month, a Bangor University research project converted David Cameron and Gordon Brown into stick figures to study their movements. Cameron's open movements -- relaxed, leaning on one elbow -- came across as more winning than Brown's tense, jabbing gestures and were found to influence voting decisions.
"Body language accounts for a great deal in influencing people's perceptions, but it should be interpreted in context -- your movements, expression and voice will betray you if you don't believe what you're saying," says Mary-Louise Angoujard, managing director of communication experts Rapporta.
Most of us process unspoken signals subconsciously, but Angoujard has pulled out some of the main 'tells' to watch out for, whether it's in deciding which political party to vote for, or in preparing your own presentation.
Hands: The politician's prop (there's even one named after former US president Bill Clinton), fluid gestures suggest you're relaxed, but limp hands imply weakness, as can open fingers.
Brown's familiar chopping hand can be effective, but it's more meaningful if it's spontaneous and can be distracting if it's too controlled.
Whether your hands are open or closed is an indicator of what's going on in your mind -- in an expressive gesture, a closed hand can be a sign of stress. If your hands are out of view, it may indicate you have something to hide.
Hands raised higher -- at chest level, say -- are more powerful, lower hands less so. Further out from the body, gestures indicate you're giving or sharing, movements close to the body suggest you're keeping something to yourself.
Left or right-handed movements -- whether you're left or right-handed, left handed movements are seen as more spontaneous and personal, those on the right are more controlled, cold and professional (these correspond to left and right brain hemispheres, according to Angoujard).
"Microscratches" -- depending on the context, tiny scratching movements can show you're feeling ill at ease. Likewise, "microcaresses" can indicate self-comfort, self protection or well-being.
Stance: Even distribution of weight and a relaxed and upright pose is confidence inspiring -- a slumped posture or rigidity can sap your authority or make you appear defensive. In the Bangor study, Brown's gestures betrayed a discomfort that was interpreted negatively. But there are more subtle 'tells', too, as Angoujard observes:
"Putting the weight on the right side can be a sign of stress around the topic -- your (right) rational side is in stress, you're not as strong as you say in every point.
"David Cameron will frequently shift weight," she says. What this says will depend on the moment of shift. Leaning to the right may suggest stress in one context, emphasis of a point in another.
A political debate doesn't give the party leaders much expansion space, but generally, roaming a stage can be distracting and rob you of authority anyway.
But moving position can be used effectively to transition from one topic to another, or as a vehicle for connecting with one side of the room. It's important to maintain eye contact with the audience, not just favouring the front row or the back but connecting with different areas by walking around.
Head axis: If your head tilts to the left, you're likely to seem sympathetic, connected; right and back is a more analytical position.
Facial expressions: The mouth can be very expressive, according to Angoujard, who notes that "Cameron withdraws his lips quite regularly, which may indicate tenseness".
She also suggests viewers watch out for the 'serpent's tongue' -- if you look very carefully, sometimes a person's tongue darts out very quickly in an unconscious gesture, like a little blow to an opponent.
Blinking frequently is a sign you're more truly engaged, while an unblinking look can give the impression you're lost in your own world or fearful.
These are just some of the body's tell-tale signs, but they come with a warning from Angoujard: body language cannot be judged in isolation -- context matters. Start by thinking about your values and beliefs, and you're likely to come across as authentic and credible. If you don't feel it, you'll just look false.