“What’s a monster’s favorite bean?”/“A human bean.”

A popular monster riddle is:
 
Q: What’s a monster’s favorite bean?
A: A human bean.
 
The riddle has been cited in print since at least 1996, when it was included in a Halloween joke list.
     
 
Google Groups: soc.culture.filipino
HAPPY HALLOWEEN
Gorgeous
10/22/96
(...)   
Q. What’s a monsters favorite bean?
A. A human bean.
 
Google Groups: maus.talk.english
Halloween Jokes
Karl-Heinz Wachtendorf
11/2/97
(...)
Q. What’s a monsters favorite bean?
A. A human bean.
 
Google Groups: alt.support.mult-sclerosis
Halloween Shorties
Bill McCartney
11/1/98
(...)
What’s a monster’s favorite bean?
A human bean.
 
Google Groups: alt.newlywed
[OT] Hallo Bean
Denise~*
10/31/00
(...)
Q. What’s a monster’s favorite bean?
A. A human bean.
   
Twitter
Lofton Staffing
‏@LoftonStaffing
Q. What’s a monster’s favorite bean?
A. A human bean.
12:27 PM - 23 Oct 2009
 
Google Books
The Ultimate Kid’s Joke Book
By Peter Coup
London: Arcturus Publishing Limited
2013
Pg. ?:
What’s a monster’s favourite bean?
A human bean!
 
Google Books
Justin’s Chuckle Time
By Justin Fletcher
London: Faber & Faber
2013
Pg. ?:
What is a monster’s favourite bean?
A human bean.
 
Google Books
Gigglers: Disgusting Jokes
By Toby Reynolds
London: Scholastic UK
2015
Pg. ?:
Q. What is a monster’s favourite bean?
A. A human bean!
 
Twitter
kvag
‏@kelseygranchie
SPOOKY JOKE OF THE DAY: what a monster’s favorite vegetable? a human bean!!!!!!!!!!!!!!!!!! 👻
7:46 AM - 6 Oct 2016