What did Stanley say was on top of the big thumb?

In "Holes" by Louis Sachar, Stanley Yelnats mentions that there was a "big thumb" on top of which he believed there was a "big, green thumb." This thumb symbolizes a sense of hope and possibility in the context of the story, representing the idea of fortune and the connection between the past and the present. The imagery reflects the themes of fate and destiny that run throughout the novel.