The project is not small. Do you really think someone will review it for free?

I'm pretty sure the free reviewer is the student Bheemamahesh.

As I understand the question, the project is not necessarily intended to accomplish anything... but it is supposed to do nothing or anything in a safe manner. And there is a bug hidden in the code to find.

Based on that, I would suggest starting with all the standard advice (strict, warn, 3-arg open, etc, etc) and take close notice of the problems that they are intended to prevent. Make a big list (Variable typos, undefined values, barewords, borked references, changing the r/w type of a filehandle, etc.)

With those kinds of problems in mind, run through the code in your head, and imagine/simulate what would happen on hostile input.