“How do you make a hamburger laugh?”/“Pickle it gently.”

A hamburger riddle is:
 
Q: How do you make a hamburger laugh/smile?
A: Pickle it gently.
 
The hamburger joke has been cited in print since at least 1978.
 
“How do you make a cheeseburger sad?”/“Make it with blue cheese” is a related riddle.
 
   
Google Books
One Hundred and One Hamburger Jokes
By Phil Hirsch
New York, NY: Scholastic Book Services
1978
Pg. 78:       
How do you make a hamburger smile?
Pickle it gently!
   
Google Books
August 1978, Boys’ Life, “Think & Grin,” pg. 66, col. 2:
Ronald: How do you make a hamburger smile?
O’Donald: Pickle it gently. — Donald Derry, Independence, Mo.
 
11 March 1983, Lexington (KY) Herald-Leader, “Kentucky Kids,” pg. D10, col. 4:
How do you make a hamburger laugh and smile?
Pickle him a little!
By Heather Leach
Auxier
 
16 February 1999, Northwest Herald (Woodstock, IL), “Jokes,” Style sec., pg. 3, col. 1:
How do you make a hamburger laugh?
Pickle it.
     
Twitter
Lubbock Fuddruckers‏
@LubbockFudds
How do you make a hamburger laugh? Pickle it gently! (Or just go ahead and pile on a bunch of pickles!) http://fb.me/z8uSpgY7
12:43 PM - 3 Feb 2011
 
Twitter
McDonald’s‏
@McDonalds
Q: How do you make a hamburger laugh? #JokeDay
10:55 AM - 1 Jul 2014
 
Twitter
madisonnn♛‏
@Guessjohnson
Replying to @ItsFoodPorn
how do u make a hamburger laugh?
PICKLE IT
8:13 PM - 15 Nov 2016
   
My Town Tutors
Hamburger Jokes: Hamburger Jokes for Kids
Posted on April 1, 2017 by mmolloy
(...)
13. How do you make a hamburger laugh?… Pickle it!
 
Reddit—Jokes
How do you make a hamburger laugh?
submitted May 27, 2017 by Shitjustgotshitty
Pickle it gently.