Body language of the two candidates is everything. One engages, the other doesn't.

When Obama used the Waving a Ball gesture during his convention acceptance speech.

In this movement, the president moves his forearm in an arc from the elbow with his palm open, fingers slightly rounded, as if he were holding a baseball. He often uses this gesture when trying to pass along a belief that he wants the viewer to embrace. ...NYT

You might be surprised when you learn which speaker -- Obama or Romney -- uses the more successful gestures, according to a New York University Movement Lab's analyst of the candidates' all-important body language.

Here's Romney:

Mr. Romney’s body language is generally more free-flowing than Mr. Obama’s. Such movements can be infectious, encouraging the viewer to join with the speaker. ...NYT

And here's Obama:

Mr. Obama uses a more controlled style than Mr. Romney does. While the force of his movements can prompt the viewer to support the argument put forth, controlled movements can also make the viewer feel that the path suggested would not be easy. ...NYT

The Times' interactive piece goes on to show the speakers during a speech and the analysis of specific gestures.

Betcha both candidates (and their designated debate worriers) have seen the analysis already.  The question remains whether either will change his style for tonight's "crucial" performance.