Fum

On December 5 and 20, fum, fum, fum!

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Fum \Fum\, v. i.
     To play upon a fiddle. [Obs.]
     [1913 Webster]

           Follow me, and fum as you go.            --B. Jonson.
     [1913 Webster]

From The Jargon File (version 4.4.7, 29 Dec 2003) [jargon]:

  fum
   n.

      [XEROX PARC] At PARC, often the third of the standard {metasyntactic
      variable}s (after {foo} and {bar}). Competes with {baz}, which is more
      common outside PARC.