How do 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 uncertainty, that is the manas thinking and investigating. When your attention is constantly on the huatou, and there is always a question in your mind—though without obvious thinking, analysis, or deliberation—and those doubtful thoughts cannot be shaken off no matter how hard you try, that is the manas investigating.
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