"What has four legs and one arm?"/"A happy…

Many people have a pit bull to protect property. A popular riddle is:

Q: What has four legs and one arm?
A: A happy pit bull.

That is, the pit bull has four legs—and someone’s human arm. The joke has been popular since 1990 (when it involved a Doberman) and 1991.

Wikipedia: Pit bull
Pit bull is a term used in the United States for a type of dog descended from bulldogs and terriers, while in other countries such as the United Kingdom the term is used as an abbreviation of the American Pit Bull Terrier breed. The term was first used in 1927. Within the United States the pit bull is usually considered a heterogeneous grouping that includes the breeds American Pit Bull Terrier,

Newspapers.com
26 March 1990, Edmonton (Alberta) Journal, “Pinsent with glass of apple juice brings back different picture” by Barry Westgate, pg. B1, col. 5:
Warming to the topic, when you ask your friends what has four legs and an arm, and they don’t know, you can tell them a Doberman.

Newspapers.com
21 July 1991, San Francisco (CA) Examiner, Rob Morse column, pg. A-3, col. 1:
Dumb joke of the day: What has four legs and an arm? A very happy pit bull.

Newspapers.com
24 July 1991, Stevens Point (WI) Journal, “NYT Lite” by New York Times News Service, pg. 12, col. 5:
CANINE CONTENTMENT
Q. What has four legs, one arm and is happy?
A. A pit bull.
—Lori Korleski Richardson, Sacramento (Calif.) Bee

Google Groups: rec.arts.startrek.current
SeaQuest DSV <> ST
Dirk Loedding
Sep 16, 1993, 12:09:00 PM
(...)
... What has four legs and an arm? A happy Pit Bull.
___ Blue Wave/QWK v2.12

Gpogle Groups: alt.tasteless.jokes
Freddy Mercury jokes
Ole Irgens
May 24, 1994, 4:37:00 PM
(...)
—SPEED 1.30 [NR]: What has four legs and an arm? A happy Pitbull

14 July 1994, Toronto (ON) Star, “Some memorable E-mail taglines,” pg. H6:
What has four legs and an arm? A happy pit bull.

Google Groups: rec.humor
Canonical List Of Animal Humor 4/5
Reality Terabytes
Aug 22, 1994, 7:40:58 AM
(...)
What has four legs and an arm?
A happy pit bull.

Google Groups: comp.lang.basic.visual
copy protection
Lars Jacobsen
Oct 21, 1994, 10:51:40 AM
(...)
* VbReader 2.01 #NR * What has four legs and an arm? A happy pitbull.

Google Groups: alt.tasteless.jokes
Abo Joke and Nigger Joke
Keith R. Fyhr
Apr 15, 1996, 3:00:00 AM
(...)
What has 4 legs and one arm?
A happy pitbull coming home from the playgrounds

Google Books
A Treasury of Gross Jokes
By Julius Alvin
New York, NY: Kensington Books
2003
Pg. 127:
What has four legs and one arm?
A happy pit bull.

Google Books
Man Walks into a Bar:
Over 6,000 of the Most Hilarious Jokes, Funniest Insults and Gut-Busting One-Liners
By Stephen Arnott and Mike Haskins
Berkeley, CA: Ulysses Press
2007
Pg. ?:
What has four legs and an arm? A happy pit bull.

Google Books
Silly Animal Jokes and Tongue Twisters!
Includes Cats, Dogs, Frogs, Toads, and Barnyard ANimals
By Mrs. Barberelli
Morrisville, NC: Lulu Press, Inc.
2019
Pg. 60:
Q: What has four legs and an arm?
A: A happy pit bull.

Twitter
Robert Wilkinson
@robertwlk
What has four legs and one arm?
A happy pit bull.
5:36 AM · Nov 4, 2020·Twitter Web App

“What has four legs and one arm?”/“A happy pit bull.”