that barely suppressed male animal seemed to peer out

An animal is not a human, if a human is described as such they are most probably brutal and bestial. This is probably the case with Scorsoni who doesn't try that hard to act in a civilised manner.

That's based on the brief excerpt you've given us, context is everything and without more context it's just a best guess.

Iz I gotta give you & Cen just a lotta credit

Thank you for your help.

"Again, that" signals that this has been mentioned before. When we say an animal seems to "peer out of someone's eyes" we are saying that a buried or hidden animal-like aspect of that person's personality is being revealed or suggested by the expression on the person's face, especially the look in their eyes. Animal comparisons are often used to suggest (often bad) aspects of personality, e.g. wolf (cruelty, fierceness) snake, rat (untrustworthiness, deceit). If I said that a person's inner snake seemed to peer out of his eyes, I mean that his expression seemed to reveal his hidden untrustworthy or deceitful nature.

I like your interpretation on the phrase. Is such an expression usual in English literally or verbally?

Most native speakers would understand such an expression even if they had never seen it before.

Thank you very much for your help all the time.