Zena, it's harder to recognize tougher testlets for AUD than it is for FAR & REG, at least in my opinion. I noticed no discernible difference in difficulty between the three testlets when I took the exam (AUD). The difficulty of FAR testlets on the other hand was much like a stepwise function; however this wasn't the case for AUD. This was particularly agonizing because I was waiting for the results of both exams simultaneously. I felt significantly worse for FAR because of the increasing difficulty (a good sign, but the exam was probably the hardest I've taken since multi-variable calculus my freshman year) which only made me doubt my performance on AUD. In the end both exams turned out about the same.
If I remember correctly, the more challenging testlets involved a higher concentration of logic questions that had multiple “good” answers, but you had to read very carefully to choose the best answer and absolutely make sure you were answering the question they were asking. Compare this with traditional definition questions which are usually more straight forward and require less judgment. An appropriate example of this would be most types of internal control or procedural evidence based questions. You might have a question where all four of the answers are proper internal control activities, but you have to choose the one which best satisfies the problem being asked.
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