Seine Antwort auf die Behauptung, er besitze vielleicht, sei aber nicht, war nur Zittern und Herzklopfen.
His answer to the assertion that he did perhaps possess, but that he was not, was only trembling and palpitations. [Kaiser/Wilkins]
His answer to the accusation that he might possess something but didn't exist, consisted of trembling and heart palpitations. [Hofmann]
Asphyxiation is the symptom of being without having, and trembling and palpitations are the symptoms of possessing without being, or at least being told that this latter might be the case. This aphorism revisits both having and being on the one hand, and answering on the other.
There are two micro-scenes that could be spun out of this aphorism. In one, someone in a position of authority is making a statement about someone else. (Behauptung does not primarily mean accusation.) The former person could be a future father in law, a judge, the latter's own father. The other micro-scene is purely introspective; a man thinks this about himself, and the thought induces trembling and palpitations.
In either case, the idea of possessing without being elicits physical signs of distress, either fear or indignation, which indicate a visceral desire or need to reject it, but no refutation. He remains silent. The idea of inverting aphorism thirty-five might have prompted Kafka to try to imagine having without being, and then to see how he might go about dramatically framing the introduction of that idea. To possess without being would mean that there is no being, at least in his case, but only a kind of registered relationship to those things we think of as part of our being. If I do not exist, but only possess, then I'm like a demon inhabiting a body, living a life, that is mine only because of some kind of contract or receipt. It would mean that everything remains as it is, or seems, but that there is no basis for what is. There would be having, but no one to have.