Briñol and petty (2003) conducted a study in which participants were presented strong or weak arguments on an issue while they were either shaking or nodding their heads to test the durability of headphones. why did head movements matter?

The answer is " It was a subtle way to make participants feel more or less confident."

When the arguments were solid, individuals who gestured or nodded their heads concurred with them more than individuals who shook their heads, on the grounds that the head nodders had more trust in the solid contentions that they heard, But when contentions were frail, head gesturing had the contrary impact, it gave individuals more certainty that the contentions they heard were powerless, making them less persuading. Thus we conclude from this that anything you can do to influence individuals to have more trust in your message will make it more compelling, as long as your contentions are solid.