Human cruelty is explored in multiple dimensions through the exchanges in chapter 4. The ending of it with Curley's wife is going to demonstrate how brutal this can be. What Crooks does with Lennie is a foreshadow to it. Crooks recognizes that he is smarter than Lennie and wishes, for a moment, to use his intellect to prove his point that a poor man of color faces additional burden and heartache than a poor white man. Lennie does not understand any of this and Crooks knows it. It is for this reason that he constructs the situation of what would happen if George left Lennie. If nothing else, Crooks' motivation is to simply have his voice heard, to have his experience validated. He wishes to come across as an individual whose pain of isolation and segregation can be felt by a white person who would never have to endure such a socially imposed condition. This becomes his primary motivation, something that is realigned when he sees that Lennie does not become sad or empathize, but rather becomes angry in the thought that something has happened to George. In this pivot, one sees how Steinbeck brings out the idea that human cruelty, while it might be focused and driven, ends up choking the life out of the individual, removing their humanity, if only for a moment, and the humanity of the target of such action.