I read an account of this incident years ago and have often wondered about it. Here's the short version: http://soultherapynow.com/articles/carl-jung.html A longer version is available at this separate source (which does not allow for copy and paste): http://books.google.com/books?id=f-...AEwBA#v=onepage&q=jung freud bookcase&f=false Jung called this phenomenon "exteriorization of emotion". I don't have a firm explanation for this incident, but I can suggest that it was some sort of folie a deax. Freud and Jung were heavily emotionally invested in each other. Jung was Freud's first non-Viennese follower at a time when he, Freud, was more reviled than anything else, and he favored Jung among his followers for it, and also for the fact he wasn't Jewish. Jung added a layer of respectability to psychoanalysis that his fellow Jewish/Viennese followers did not. They openly described their relationship as Father-Son, but the father was rather dependent on the son. The first noise from the bookcase may have been natural creaking that happened to coincide with Jung's angry solar plexus. The second, 'confirmatory' noise, though, may have been an hallucination induced by Jung's announcement it would happen. As you can see from the second link, Freud felt Jung's presence and belief had unduly affected him.