In psychological criticism, some writers identify the pen with the male phallus in theories of creativity.  (Quick www reference)   Regardless of the details, the idea is that if you lack access to the phallus somehow, you won't have access to the pen and sometimes vice-versa.  If someone explored this approach, it might reveal why Old Cotter can't find  the words to finish his sentences.

    And it might help show that the boy has the propensity for wisdom, that language forms within him in ways that offer deep levels of meaning, if he can find a way to them.

    That's all on this for now.  If more stories get up on this site, there should be more phallic discussion.  To use this kind of interpretation, you've got to show that it works throughout a whole story, or group of stories.  One incident isn't enough.

    I still don't get the point you're making about imbecile