Lazzi
(singular: lazzo) are all those items
in a comedian's bag of tricks
used to get a laugh, fill in a sketchy scene, or just irritate the heck out a fellow
comedian all the while keeping the audience entertained. [Duchartre] devotes a chapter
to the subject.
[Griffiths, pp. 18-19] distinguishes between a lazzo, a 'funny moment' or gag,
and a berle (from which we get the word 'burlesque'), more complex and involved
in the plot.
This one might be called the 'ambush the musician' lazzo.
*berle = 'practical joke,' lazzo = 'smaller piece of
comic business' [Oxford: 'Italy,' 'Commedia dell'Arte,' iii.Economy of the Companies (p.401)]