How does Steinbeck convey Lennie's animal-like qualities in Of Mice and Men?
Lennie is described as being animal-like several times in the first few pages of the book. Steinbeck writes that Lennie "walked heavily, dragging his feet a little, the way a bear drags his paws" and that he drinks "snorting into the water like a horse." When George demands Lennie hand over the dead mouse, Lennie brings it "slowly, like a terrier who doesn't want to bring a ball back to its master." By establishing the connection early on, Steinbeck emphasizes its importance.
Lennie is also associated with animals frequently: he carries mice in his pocket, wants to "tend the rabbits" on their future farm and can barely be kept away from his new puppy. Like the animals he is surrounded by, Lennie is innocent. He acts on instinct and therefore cannot really be held accountable for his actions. Like the mice and puppy, he is a victim of his own strength and of a cruel world.
Penelope3907 does a great job pointing both to specific instances in the text where Lennie is directly described as having animalistic qualities and to motifs of association wherein Lennie is repeatedly aligned with mice and dogs and a sense of closeness with animals.
Late in the novel, when Lennie is fleeing alone from the scene of the murder, he is again described in distinctly animalistic terms.
"Suddenly Lennie appeared out of the brush, and he came as silently as a creeping bear moves."
In this scene Lennie's attitude/behavior at the stream is highly animal-like and he is surrounded by wild creatures - a heron, a small bird and a snake. Here then we have both the associative motif connecting Lennie to animals and a direct description of Lennie's animalistic qualities.
Given the repeated and insistent connections made in the text between Lennie and a certain animalism, we might ask what this means. What is the significance of Lennie's animalism?
There are many ways to interpret Lennie's character in this light, but one compelling reading suggests that Lennie's animalism functions as a counter-part to George's social savvy.
Furthermore, insofar as Lennie is attached to George, Lennie's "naturalness," so to speak, hampers any social progress or social integration that George might make.
The simple dreams that George fosters for himself individually are complicated by Lennie. George's desires for going in to town for a drink or finding a girlfriend are compromised by George's bond with the animalistic Lennie.
Notably, when Lennie is killed, the first thing George does is to head into town for a drink. He leaves the brook, with its natural life and its avatar/symbol (Lennie), and makes his way toward a socialized world.
Again, there is more than one way to understand Lennie's significance as an animalistic character. This is just one argument among many.
Another way to see Lennie's animalism is to read his connection to the natural world as a suggestion that Lennie is not "innocent" in a conventional sense. He is capable of real violence - as any animal is - and thus is best seen, not as an innocent victim of circumstances, but as an impulsive being who lives (slightly) outside the bounds of human morality.
Lennie's death is then a symbolic death wherein the unthinking wildness of nature is quite starkly delimited and severed from a human, social world.