but SSR makes them squawk
Correct me if I am wrong (story of my life) but I believe the genesis of transponder codes was during WW2 when they were known as Identification Friend or Foe (IFF for short). In the hope that Germans listening in to RAF frequencies could be fooled, various code names were invented. Thus the code name for IFF was "Parrot." And the code name for transmit was "Squawk."
When RAF controllers wished to tell pilots to switch to a new frequency they would say "Squawk Channel Able
If they told the pilot to switch off his transponder the code word was "Strangle" Thus "Strangle your Parrot"