No system of conjugal relations is perfect.

Mr Verloc presumed that his wife had understood him, but he would have been glad to hear her say what she thought at the moment.

It would have been a comfort.
There were several reasons why this comfort was denied him.

There was a physical obstacle: Mrs Verloc had no sufficient command over her voice.
She did not see any alternative between screaming and silence, and instinctively she chose the silence.

Winnie Verloc was temperamentally a silent person.