Types of Head Shakes
A fast and rhythmic head shaking definitely says - "no, I disagree, this is not true."
A slow and irregular turning of the head usually signals misunderstanding.
Something didn't get through quite right.
Slow and rhythmic head shaking can also signal disbelief. We cannot accept what we just heard.
So far so good, but sometimes the head shake is only barely visible. It can be quick or nonchalant, it doesn't require a "complete" head shaking from side to side , a single turn of the head still can signal "no" - as if the listener got slapped by the words he just heard. I mention this because most people avoid shaking their heads like a cartoon character, and often culturally raised with the idea that it's impolite or inappropriate.
When we converse on serious matters we often prefer to look to the distance, it helps us concentrate and think more clearly, it's not because we dislike the person we speak with or his words - it's simply a switch from conversing to processing.
When we don't like what we hear however, we try to engage as little as possible and strive to end the talk. We show other impatient gestures such as glancing to the sides, tapping or playing with objects and if we participate we do it with minimal effort by throwing meaningless remarks.