I'm currently reading Harry Potter und der Gefangene von Askaban to improve my German. In the English version, Harry gets on a Wizarding bus called "The Knight Bus" after running away from home. This is a pun in English, as "knight" sounds like "night". The translators usually make an effort to either preserve any puns they come across, or if they are untranslatable will add a new one.
In the German version, the Knight Bus is called "der Fahrende Ritter". I understand the meaning of the German translation, "the travelling knight".
However I don't understand the joke - can anyone help?