It's all about looks.
Durham University professor Tim Clark believes any slip-ups by Gordon Brown, pictured, David Cameron or Nick Clegg, could overshadow their arguments.
Prof Clark, an expert in public speaking, said: "You can have the best presentation, but not the best message, and still come across well."
During the televised debate Prof Clark believes there will be strict rules in place on how audience members react.
He added: "This response doesn't have to be applause, but could be laughter following a comment.
"If audience members give a negative response to one of the leaders, this is likely to have more impact on the viewers at home."