Tom, being the most clever and smart altogether of those who heard Mike’s speech, and knowing well enough what are all the Corleones like, despite their not knowing it themselves, was the least surprised. Here’s the quote from novel: “All four heads turned and stared at him. Clemenza and Tessio were gravely astonished. Hagen looked a little sad, but not surprised. He started to speak and thought better of it.”
There are many interesting things written about this scene in the novel. Just read it – I would love to post everything, I think only that our local Higher-Ups will not approve of me. But the genesis of Mike’s decision is also very interesting. When he goes to see Kay before visiting the hospital, still thinking all this had nothing to do with him, we read: “Thinking this made him feel guilty about not feeling more sympathy for his father. His own father shot full of holes and yet in a curious way Michael, better than anyone else, understood when Tom said it was just business, not personal.”
But after the phone talk with Sonny in the hospital, “For the first time since it had all started he felt a furious anger rising in him, a cold hatred for his father’s enemies.”
After his scene with McClusckey, “He saw the captain give him atriumphant glance and he tried to answer that glance with a smile. At all costs he wanted to hide the delicious icy chilliness that controlled his brain, the surge of wintry cold hatred that pervaded his body. He wanted to give no warning to anyone in this world as to how he felt at this moment. As the Don would not.”
He was not only discovering his own true nature. He made it his rule already to take everything in this world personal. And he new that both were dead men.