Watchman or Donkey

Student:—“Herr Nachtwächter (nightwatchman), I wish to ask you something. May I call a Nachtwächter a donkey?”

Nachtwächter:—“Just you take yourself off, before I haul you in.”

Student (goes, but returns after a few steps):—“Now listen; I have another question. May I call a donkey a Nachtwächter?”

Nachtwächter:—“You may, for all I care!”

Student:—“Well then, good-night, Herr Nachtwächter!”