Many times it is impossible to prove legally that a certain individual is a communist; but for cases of this sort I recommend a practical method of detection--the "duck test." The duck test works this way: suppose you see a bird walking around in a farm yard. This bird wears no label that says "duck." But the bird certainly looks like a duck. Also he goes to the pond and you notice he swims like a duck. Then he opens his beak and quacks like a duck. Well, by this time you have probably reached the conclusion that the bird is a duck, whether he's wearing a label or not.
Credits: Richard C. Patterson, 1949, quoted in
Walter LaFeber, Inevitable Revolutions: The United