I believe  " He paused, then in a low, sinister voice he said slowly: "Sometimes I believe that you would sell us!" Mrs. Vandemeyer smiled and shrugged her shoulders.
He sometimes believes that Mrs Vandemeyer would sell them or trade them for something of lesser value.
mnli hypothesis: He sometimes believes that Mrs Vandemeyer would sell them or trade them for something of lesser value. premise: I believe  " He paused, then in a low, sinister voice he said slowly: "Sometimes I believe that you would sell us!" Mrs. Vandemeyer smiled and shrugged her shoulders.