A pigeon... "Coup, coup"
Because they have bills.
They Can Both fly except the fridge.
I got Kniiiiiives on it! that inspired the joke.
Batteries have a positive side! inspired by: http://www.reddit.com/r/Jokes/comments/2zlrot/howmanyfeministsdoesittaketochangea/
RPM (Revolutions Per Minute)
Both are measured in revolutions per minute.
Coup.
One has a coo, the other has a coup
For staging a coo
A STOOL Pigeon