mmm

An emotional expression of satisfaction.

Mmm, this is a tasty pie!

An expression used to show thought, reflection, or confusion.

Mmm, I see what you mean.

In his final years he [John Ogdon] gave an interview to an American journalist who noticed that “his handshake is a boneless fadeaway. His response to a lengthy anecdote from a close friend is likely to range from a non-committal ‘Mmmmmmm’ to a rare ‘Very interesting’.”

Used to represent an utterance that is muffled or spoken with a full mouth (also spelled "mmph").

Yes.

Danny: Have you got any food? I: Mmm! As a matter of fact, got a saveloy.