The dead mouse, or mice, that Lennie carried around with him in the novel 'Of Mice and Men' is an important image, all the more so because mice are actually mentioned in the title of the novel by John Steinbeck. It refers to 'the best laid plans of mice and men' that too often go wrong from the poem (although he too 'borrowed' the phrase) by Robert Burns. One of the messages it portrays is the sad, pathetic dreams that the men share of getting out of their labor-camp bondage situation of the Depression and becoming land-owners and free men themselves.
Learning-challenged Lennie still continues to pet the soft mice even after they are dead showing his lack of understanding about the concept of death and decay which mirrors his lack of understanding of the unavailbilty of the dream and of the consequences of his rough well-meaning actions.
One of the conflicts between Lennie and George revolved around Lennie carrying a dead mouse in his pocket. Lennie carried it with him because he liked to pet it. The fact that the mouse had died did little to take away from the enjoyment Lennie had through petting the creature.
In Of Mice and Men, Lennie, a mentally disabled man, has a fascination with "soft things." To satisfy this urge to pet soft objects he would always carry around a dead mouse in his pocket. This angers George and he forces Lennie to throw it out. Later in the novel Lennie has the opportunity to be around Slim's puppies. Slim gives Lennie one of the puppies and allows him to pet it as much as he wants. When the puppy nips Lennie, he accidentally kills it, by using his super strength. Due to Lennie's mental disability he is not aware of his own strength which ultimately causes him to kill all of the "soft things" he likes to touch. (Ex: mice, Curley's wife's hair, and the puppy)