Many experts have already analyzed Zuckerberg’s Tuesday remarks about data privacy and apologizing for his company’s mistakes. But just as important as what Zuckerberg said was how he said it.

I examined Zuckerberg’s body language closely throughout the lengthy testimony. While the CEO was skillful in staying calm, answering questions, and visually presenting himself, he was less successful in his use of body gestures and supporting staff. The performance overall was a mixed bag.

For the most part, Zuckerberg comported himself as I expected: He was respectful, calling everyone “senator”; patient, even when the questions made no sense or had been asked many times before; and contrite.

As to be expected for someone not expert in public speaking, Zuckerberg showed signs of psychological discomfort. When he first sat down he was uncomfortably stiff and hesitated to look around. He took his first sip of water so slowly that I had time to check my Facebook and Twitter accounts before he was finished. He took hard swallows every once in a while, a telltale sign that someone is under stress. Zuckerberg compressed his lips many times, another sign of stress. People who testify before Congress often compress their lips repeatedly. His blink rate was higher than normal when he first started—above 50 beats per minute—but the rest of the time it was in the 30s, which is still elevated but less so.

Interestingly enough, the most psychological discomfort I saw on Zuckerberg’s face, as evidenced by simultaneous lip compression, eye squinting, and narrowing of the glabella (the area above and between the eyebrows), was when he was trying to decipher vague or unintelligible questions from the senators.

Zuckerberg dressed as required to manage perceptions, wearing a navy blue suit and white shirt. It’s good that he didn’t show up in his signature T-shirt. But he could have done better in other areas related to his physicality.

Leaders need to use broad, smooth, emphatic hand gestures to make points. Out of habit, Zuckerberg used his voice for emphasis; that was a mistake. Gestures are more powerful than words when employed skillfully.

But that wasn’t the only visual problem: The Facebook officers sitting behind Zuckerberg were often a distraction to his presentation, talking, laughing, and even checking their smartphones as the testimony wore on. Joel Kaplan, Facebook’s vice president of global policy, squinted when he heard questions he didn’t like and sometimes looked as if he were trying to recollect facts. Myriah Jordan, Facebook’s public policy director, flicked her fingers and hid her thumbs when questions bothered her, and pursed her lips or pulled them dramatically to the side to show discomfort or disagreement with something she heard. They were an easier read than Zuckerberg was as to which questions or answers were an issue. They even showed how they favored certain senators, such as Orrin Hatch, over others by relaxing their faces.

While his deputies gave up a lot of nonverbal information that experts can notice, Zuckerberg kept a poker face. This goes to show that in a theater production it is not just the lead actor who matters, but everyone on the stage.

Zuckerberg did not come across as deceptive in his testimony. Yes, there were moments of anxiety, nervousness, tension, and dislike of questions, but that tells us little. In such a setting, displays of psychological discomfort are only natural. Overall, Zuckerberg came across as authentic and humbled—a positive outcome for him, his company, and its shareholders.

The social media prodigy was fortunate to complete his first day of questioning without any visible wounds. Zuckerberg is a quick learner, and I have no doubt that in time he will master the art of public presentations to a global audience.

Joe Navarro is the author of What Every BODY is Saying: An Ex-FBI Agent’s Guide to Speed-Reading People.