In this context, it means nothing. As you point out, GP is conflating pitch with pitchless phonemes, for example, the phrase &quot;<i>we say &quot;Mmmmm&quot; not something higher pitched</i>&quot; doesn&#x27;t make any sense.<p>However, I suppose GP meant to write &quot;<i>we tend to say &quot;Mmmm&quot; with a specific, relatively low pitch</i>&quot;, a statement with which I don&#x27;t particularly agree. I would rather say it&#x27;s done at an average conversational pitch, or even at a higher pitch since it often has a pitch accent conveying surprise. Which I believe is the main purpose of saying &quot;mmm&quot;: communication, not vibrational tongue massage. Consider that when you say &quot;mmm&quot;, you voluntarily choose a pitch intonation according to what you&#x27;re trying to convey, ie. how pleasantly surprised you are.