Sentence:  But if the Trial did not expose the special Nazi mania so deadly to Jews as well as to anyone upon whom it <WSD>happened</WSD> to light , neither did it warn very effectively against the ordinary anti-Semitism of which the Nazis made such effective use in Germany and wherever else they could find it . 
Meaning of the word marked with <WSD> tags:  chance to be or do something, without intention or causation