Sentence:  And the bed that sagged in a certain place where all the weight had been put too many times before and the walls fine and thin for overhearing talk in the next room when Gratt went out for ice , the sound coming through the walls like something on the other side of the curtain , so you <WSD>knew</WSD> they heard you when they were quiet and while you lay wondering what they had heard you listened . 
Meaning of the word marked with <WSD> tags:  be cognizant or aware of a fact or a specific piece of information; possess knowledge or information about