Chapter five of "Of Mice and Men" begins with an accident. Why did it happen and what consequence does Lennie fear?this is from mice of men

In Chapter 5, Lennie has killed his puppy. At the beginning of the chapter he is staring at its dead body saying, "Why do you got to get killed? You ain't so little as mice. I didn't bounce you hard." In other words, like the mouse and the girl in Weed, Lennie did not recognize his own strength and it resulted in tragedy for Lennie. Although Lennie is upset about the death of his puppy, he is more concerned about what George will do. He is afraid George will say, " No jus' for that you don't get to tend no rabbits!" At that point, he is furious at the puppy for dying. He flings the puppy from him and says, "Now I won't get to tend the rabbits" And like a child he rocks himself back and forth. Unfortunately, the dead puppy is the least of Lennie's problems because soon after, Curley's wife appears and asks what Lennie is hiding.