I'm reading The Good, The Bad and The Smug by Tom Holt. It's a British-style fantasy/comedy in the Hitchhiker's tradition, and is good so far (page 89). But, something is throwing me: often a character will respond to a question by saying a single word which is written in the book as "Mphm". It isn't a single person saying this; I've counted at least three, so it must be something everyone's supposed to understand. Unfortunately, the set of those who understand doesn't include me.
My attempts to pronounce it founder; either I come up with "mm-p-'hmmm" (if the "p" is pronounced separately), or "mm-'fmmm" (if the "ph" is pronounced as "f").
My best guess is that it's the equivalent of my saying "Mhmm", pronounced "Mmmm-hmmm", and meaning "yes". I still have no idea of how it is to be pronounced, though.
Is my guess on the meaning correct? How would this be pronounced? And, any idea of how this spelling originated?
Edit: here's some example text from the book. Norman is objecting to being coerced into being an experimental subject:
"Now come on," he said reasonably. "Where's your scientific method? We can't just run bull-headed into a manned test programme, we've got to work up to it gradually, in controlled phases. Scientifically," he added hopefully.
"Scientifically?" Derek queried.
"Mphm." Norman nodded firmly.
Edit: I've been playing around with Google Ngram Viewer. Although there is slight usage of lower-case "mphm" in the mid-1800s, uppercase "Mphm" only starts being used in the 1900s, with the general "English" corpus having its biggest peak at 1917 (0.00000236% of words). But, if you switch to the "English Fiction" corpus, there are no usages of the lowercase "mphm", and the peak is at 1904 (0.0000128%, or five times higher).
And, if you try Google Books, you'll find a number of uses just like the ones I found in the Tom Holt story (although a lot of them are from the same World War I story).