“What instrument does a skeleton play?”/“A trombone.”

A popular Halloween riddle about skeletons is:
 
Q: What instrument does a skeleton play?
A: A trombone.
 
The joke has been cited in print since at least 1976.
 
     
Google Books
Biggest Riddle Book in the World
By Joseph Rosenbloom
Illustrated by Joyce Behr
New York, NY: Sterling Publishing Company, Inc.
1976
Pg. 134:
What musical instrument does a skeleton play?
The trombone.
 
29 October 1982, St. Cloud (MN) Times, “Just for Laughs,” Pennywhistle Press, pg. 4, col. 4:
Question: What instrument do skeletons play best?
Answer: Trombones.
Sent in by: Bobby and Karie Lucas
Ages 8 and 14
Lansing, Michigan
   
21 February 1993, Daily Chronicle (DeKalb, IL), “A Little Bit of Humor,” pg. 19, col. 2:
Jeanette: What strument does a skeleton play?
Jeremy: The trombone.
 
Twitter
Trisha
‏@mom2twinsplus1
@trillian1117 here’s another one: Q: What kind of instrument does a skeleton play? A: A trombone! #lunchboxjokes
10:50 AM - 15 Oct 2009
 
Google Books
The Mammoth Book of Really Silly Jokes:
Humour for the whole family
By Geoff Tibballs
London: Constable & Robinson Ltd
2011
Pg. ?:
What musical instrument does a skeleton play?
The trombone.
 
Google Books
Funny Halloween Jokes For Kids
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
What instrument does a skeleton play?
A trombone!
 
Reddit
What instrument do skeletons play? (self.SkeletonJokes)
submitted September 22, 2015 by Cheaselord
Trom-BONE.