How is Muley Graves characterized by animal imagery?

When Tom Joad, along with the former preacher, Jim Casy, returns to the property he once called home, he finds it completely abandoned. Not a soul he used to know, neither friend nor family member, is anywhere to be found at first. Then Muley Graves, an old neighbor, appears in the shadows, walking towards them.
Truculently, Muley tells Tom and Casy what has happened to make their former home a ghost town. He recalls how the emissaries of the bank, using their tractors like tanks, forced the people off their ancestral land and how he personally refuses to leave.
Not only were the people displaced, they were also subjected to callous treatment. The tractor drivers plowed on, disregarding any and all of the history of ground they churn over. Muley remembers the history, however. In doing so, he likens himself to two animals: a buck deer and a billygoat. He points out key locations of his past to Tom and Casy:
"Like there's a place over by our forty; in a gully they's a bush. Fust time I ever laid with a girl was there. Me fourteen an' stampin' an' jerkin' an' snortin' like a buck deer, randy as a billygoat."
Muley goes on to mention his father’s fatal injury. His father is killed by a bull:
"An' there's the place down by the barn where Pa got gored to death by a bull. An' his blood is right in that groun', right now. Mus' be. Nobody never washed it out. An' I put my han' on that groun' where my own pa's blood is part of it."
All three of these animals, buck deer, billy goat, and bull have something in common: associations with male virility.
The fact that Muley’s father is killed by a stronger male animal does not bode well for his son. In fact, Muley’s own name is indication that he will be the last of the line. Mules are typically unable to reproduce.
Tom and Casy express dismay about what has happened and concern for the person Muley has become: scared, flight-prone, and vengeful. When a car approaches, but is still quite far away, Muley barks at Tom and Casy to hide themselves. Tom is surprised by Muley’s timidity.
Muley eventually replies:
"Yeah!" he said. "I was mean like a wolf. Now I'm mean like a weasel. When you're huntin' somepin you're a hunter, an' you're strong. Can't nobody beat a hunter. But when you get hunted—that's different. Somepin happens to you."
Before the upheaval, Muley compares himself to a wolf, another virile animal and one renowned for its preference for living and hunting in packs. But now Muley has no pride in his own male-ness and his “pack” has dispersed.
No longer a wolf, Muley now identifies with a weasel, an animal frequently associated with spite and cunning. Muley is aware that he is no longer the strong hunter, the wolf, but the conniving and vengeful weasel.