OK .. I did a post not so long ago about why (imo) it's not good to start your sentence with the word "so" - tldr - it's because I think it makes a person sound stupid (other opinions are available).
I can't imagine why this one got by me! What was I thinking?
Well this is it!
When someone who is explaining something that ser wants you to believe (or because they think that you are stupid) they nod in the affirmative to reinforce their belief (and hopefully bring you around to their way of thinking).
The polite thing to do is not to immediately punch them in the face because it's creepy but to say politely "why are you nodding like an idiot?".
The same applies to idiots who shake their head in their attempt to coerce you around to their way of thinking (in the negative obviously; but this one is more rare).
Also, whilst I'm on this subject, people sometimes change the inflection at the end of a statement, turning it into a question.
Why do they do that? Is it because they are not confident of its veracity? Full of self-doubt?
If it's a form of emphasis then the emphasis is succeeding in giving me the wrong impression.
In my experience these are very AMERICAN phenomena.
Just because the USA is a powerhouse of economic activity doesn't mean we have to adopt their STUPID idiosyncracies.
I think I'm turning into a grumpy old man!
Already am in fact.