Like Martin, I don't know what to think. I started this book almost by accident and finished it by compulsion. The writing is wonderful. It's the plot I don't know what to think about. When, in an early scene, a sword shows up, I wondered whose head will be cut off with it. Chekhov would insist that the sword be used and the title suggested how. I now think that the severed head refers to how distant the intellectual point of view is from the reality of the human comedy or tragedy or what ever its genre. Either that, or the process of separating ones reason from morality. Somehow this is connected with psychoanalysis, that being the psychoanalysis of the 60s when this was published. Maybe Judaism is involved in this separation as well. It symbolizes a disturbing foreignness, an ugly reality that must continually be fled with convention or alcohol or else denied. Honor Klein is at home in it (if she's at home anywhere) but who else would be willing to join her? Which will win: civilization, or it's discontents?

When Georgie's hair shows up in a box, I figured her head couldn't be far behind. Honor Klein (whose name always made me think of Anna Freud crossed with Melanie Klein) describes herself as a severed head late in the book, she meaning it as an object used in divination by alchemists, an object of fascination but always alien. She seems to be always unknown, Never reacting in a conventional way and thus impossible to think about in a worldly context. A relationship with her would not be about happiness as a worldly one would be.
If it turns out the sword is never actually used (I don't feel like spoiling this), since it appears as a symbol in dreams and elsewhere, the idea of it is used so Chekhov can't complain. (In Iris Murdoch's The Bell, the idea of the bell is much used too and when it is told to predict death, I kept wondering who would die.)

Martin wouldn't know what to think because his thinking is severed from his feeling. Martin spends most of the book avoiding actual choices and actions. When he does make decisions, other than those forced on him, it's usually with the excuse of being drunk and they are often violent ones. For much of the plot he is either submitting to humiliations or plotting to escape from them. In the end--well, you read it and see if you know what to say.