Final answer:
In Agatha Christie's mystery novels, Hercule Poirot refers to his brain as his most valuable tool for solving crimes.
Step-by-step explanation:
In Agatha Christie's mystery novels, the detective Hercule Poirot often refers to his brain as his most valuable tool. He emphasizes the importance of careful thinking and analysis in solving crimes. Poirot believes that using his intellect and understanding human nature allows him to see through disguises and uncover the truth behind the mysteries he investigates.