Illuminator - Pt.1 Ch. 7

"Your worst enemy, he reflected, was your own nervous system. At any moment the tension inside you was liable to translate itself into some visible symptom. He thought of a man whom he had passed in the street a few weeks back ; a quite ordinary-looking man, a Party member, aged thirty-five to forty, tallish and thin, carrying a brief-case. They were a few metres apart when the left side of the man's face was suddenly contorted by a sort of spasm. It happened again just as they were passing one another : it was only a twitch, a quiver, rapid as the clicking of a camera shutter, but obviously habitual. He remembered thinking at the time : That poor devil is done for. And what was frightening was that the action was quite possibly unconscious. The most deadly danger of all was talking in your sleep. There was no way of guarding against that, so far as he could see. "

In this passage, Wilson describes how your worst enemy was your own nervous system. Reflexive instincts like the urge to scream obscenities or to distort your face can give you away. Nasty habits can reflect upon your thoughts and can lead to being charged for Thought Crimes. The thing Winston most feared was saying things in his sleep, things that were totally out of his control, and if the Thought Police were to hear him, he would face conviction which led to death.