“Why are pianos so hard to open?”/“The keys are inside.”

A popular piano joke is:
 
Q: Why are pianos so hard to open?
A: The keys are inside.
 
“She really could not play when requested. The piano was locked up and the keys were inside” was cited in print in 1881. “Can’t you open it (the piano—ed.)?”/“No, The keys are inside” was called an old joke in 1940.
 
 
Old Fulton NY Post Cards
23 September 1881, Geneva (NY)

, “Fun, Fact and Fancy,” pg. 1, col. 8:
She really could not play when requested. The piano was locked up and the keys were inside.—Andrews’ Queen.
   
3 December 1940, Nebraska State Journal (Lincoln, NE), “Pop” comic strip by Miller Watt, pg. 17, col. 2:
SON: WHY CAN’T YOU PLAY MY PIANO, POP?
POP: I’VE LOCKED IT.
SON: WELL, CAN’T YOU OPEN IT?
POP: NO. THE KEYS ARE INSIDE.
SON: THAT’S AN OLD ONE!
POP: SO’S THE PIANO!
 
Google News Archive
11 December 1946, Sydney (Australia) Morning Herald, “Best Jokes,” Playtime, pg. 8, col. 1:
Why can’t you open a piano?
Because the keys are on the inside.
 
Google Books
Jokes, Puns, and Riddles
By David Allen Clark
Illustrated by Lionel Kalish
Garden City, NY: Doubleday
1968
Pg. 233:
Conductor: Will you please open the piano?
Pianist: I can’t. The keys are on the inside.
 
29 June 1969, Sunday Advocate (Baton Rouge, LA), “Jumble” (word puzzle), pg. 10-E, col. 7:
Why it might be difficult to open a locked piano—
THE KEYS ARE ON THE INSIDE
 
13 June 1971, Boston (MA) Herald Traveler, “Joke Box,” Young Folks Page, col. 7:
Orchestra conductor: Open the piano.
Pianist: I can’t. The keys are inside.
From MICHELE DeLaBRUERE
Exeter, N.H.
   
Google Books
September 1983, Boys’ Life, “Think & Grin,” pg. 82, col. 3:
Cliff: What makes opening a piano so difficult?
Biff: I don’t know. What?
Cliff: The keys are on the inside. — Kevin Bethea, Charlotte, N.C.
   
Twitter
BlokesLib
‏@BlokesLib
Why are pianos hard to open? ... ... Cos the keys are inside! *ok ok smacking myself for that one
7:01 AM - 18 Jun 2009
 
Twitter
Only Joking
‏@avinalarf
Why is it so difficult to open a piano? Because all the keys are inside
8:11 PM - 1 Sep 2009
 
Google Books
1001 Kid’s Jokes
By Kay Barnham
London: Arcturus Publishing
2016
Pg. ?:
Why are pianos so hard to open?
The keys are inside.