How to Know That the Manas Is Applying Effort, Investigating, and Deliberating?

How can you know that the manas is working hard, investigating, and deliberating? When you feel that there is always a huatou in your mind—a questioning doubt or lingering uncertainty—that is the manas thinking and investigating. When your attention is constantly fixed on the huatou, and there is always a question in your mind, even though there is no obvious thinking, analysis, or deliberation, yet those doubts and thoughts cannot be shaken off no matter how hard you try—that is the manas investigating.