Bertha has been behaving more than ever like a madwoman, and George’s powers of credulity are very nearly exhausted.
There was as yet nothing definable in the situation, which might well resolve itself into a huge joke on the part of the other two; but Lily had a vague sense that the subject of their experiment was too young, too rich and too credulous.
There are no more uses of "credulous" in the book.
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The trick would fool none but the most credulous.
She is so credulous she believes everything she reads.