(Reuters) - U.S. presidential debates are often as much about body language and aesthetics as they are about issues and substance.

White House hopefuls Barack Obama and John McCain went back and forth in Tuesday’s debate, often pointing at each other in accusatory fashion while walking around the debate space, speaking directly to the assembled audience.

Both candidates chafed at the rules of the debate, which their campaigns had jointly agreed, and agreed partway through to loosen the format and allow further rebuttals.

McCain, a Republican senator from Arizona, and Obama, a Democratic senator from Illinois, hugged at the end of their debate. Below are other examples of body language exhibited by both candidates on Tuesday:

MCCAIN

- The Arizona senator, who avoided looking at his opponent in their first debate, directly addressed Obama and referred to him as “that one” at one point when describing the Illinois senator’s vote for an energy bill that McCain opposed.

- McCain sometimes came too close to audience members, a few of whom appeared uncomfortable by his distance. He defused that later, patting the back of one questioner, who shook the senator’s hand.

- McCain smiled broadly at many times during his exchange with Obama and lowered his voice to a partial whisper for emphasis on some issues. He did not always know where to stand when Obama was speaking, settling at one point on a position of leaning with one hand against the high chair.

OBAMA

- The Illinois senator, who referred repeatedly to his opponent as “John” during the first debate, called him “Senator McCain” throughout most of Tuesday’s exchange.

- Obama waited patiently during McCain’s attacks, comfortably perched on the stool-like chair, often smiling in seeming wonderment about what he was hearing from his opponent.

- Obama at times appeared irritated and occasionally paused or sighed before giving his answer. He was less inclined to make jokes than McCain, whose own attempts at humor sometimes worked and sometimes didn’t.