Of Mice and Men- Unfortunate misunderstanding

So Curley sees Lenny smile after he is getting into it with Carlson. Lenny is smiling because he is excited about owning a house having nothing to do with Curley. Unfortunately this provokes a fight between the two of them. It is really George's fault Lenny got involved. He told Lenny to do it. It is clear that Lenny doesn't think for himself.

Of Mice and Men- Predictions...

So first I think that Lenny may get tempted by Curley's lady. It is possible she's slept with many of the workers behind his back. Second I think that Slim, who seems like a nice leader has Curley in his group. He mentioned having two bad eggs in his group. If Curley and George and Lenny are in the same group that will cause a lot of tension because Curley is threatened by Lenny's size. It is dumb for him to be threatened by someone just because they are large, we know that he doesn't pose a threat and has a sweet nature, and is probably too dumb to cause trouble.

Of Mice and Men- Unanswered Questions

So. I just started reading Of Mice and Men. I am at the part where George and Lenny start a new job. George is covering for Lenny claiming that they are cousins and he had a brain injury as a child that made him dumb. It seems like Lenny has special needs. What is wrong with him? How did it happen and was he born with a cognitive disability or did something make him that way. Since we know they are not related, what interest does George have in protecting him? Why does he care so much for someone that he is not related to or in a relationship with? What time in history does this story take place?