“In what key does the ghost play piano?”/“In the spoo-key.”

A ghost riddle about music was posted on Reddit—3amjokes on July 4, 2017:
 
Q: In what key does the ghost play piano?
A: In the spoo-key.
     
 
Reddit—3amjokes
In what key does the ghost play piano? self.3amjokes
Submitted July 4, 2017 by edder24
In the spoo-key.
 
Twitter
Eddie Khaymovich‏
@dat_dumbass
In what key does the ghost play piano?
...
In the spoo-key.
12:32 AM - 4 Jul 2017
 
Twitter
3AM‏
@3AM_Jokes
In what key does the ghost play piano?... In the spoo-key.
12:58 AM - 4 Jul 2017
 
Twitter
LOL Tweets™‏
@lolmgco
In what key does the ghost play piano?
In the spoo-key.
2:43 AM - 4 Jul 2017