Does "think" mean "think about" or "think by" in "The Secret of Father Brown"?

Question

In "The Secret of Father Brown" by G. K. Chesterton, Father Brown was saying that he prefers studying the murder from inside not outside:

I don’t try to get outside the man. I try to get inside the murderer. . . . Indeed it’s much more than that, don’t you see? I am inside a man. I am always inside a man, moving his arms and legs; but I wait till I know I am inside a murderer, thinking his thoughts, wrestling with his passions; till I have bent myself into the posture of his hunched and peering hatred; till I see the world with his bloodshot and squinting eyes, looking between the blinkers of his half-witted concentration; looking up the short and sharp perspective of a straight road to a pool of blood. Till I am really a murderer.”

Does "think" here mean "think about" his thoughts or "think by" his thoughts as we are the same person?

And what's meant by "hunched and peering hatred", as I never met such a posture with such a feeling?

Answer 1

In the phrase "thinking his thoughts", "think" means neither "think about" nor "think by". It means having the same thoughts, holding the same thoughts in your mind. This is part of being "inside" the murder: Father Brown tries to experience the murderer's thoughts in order to better understand him.

The "posture of his hunched and peering hatred" would be a posture that is distorted by the murderer's thoughts and passions. These emotional stress caused by these thoughts and passions can cause physical stress, which may result in a change in posture. The phrase also reminds me of the phrase "warped mind", which can also be found in the Bible, Proverbs, 6:14:

With a warped mind and twisted heart, he constantly looks for his own gain at others’ expense, causing friction everywhere he goes.

However, I cannot prove whether Father Brown (or G. K. Chesterton) had the psychosomatic effect or a Biblical reference in mind, or perhaps even both.