The Question and Answer section for Of Mice and Men is a great resource to ask questions, find answers, and discuss the novel.
Slim finds it odd that the two men are traveling together, which in itself is odd. He finds George's situation even stranger when he learns George and Lennie aren't even related.
George explains that he was friends of the family, and Lennie's,...
George told Lennie to jump in a river, even though he knew Lennie couldn't swim. Lennie almost drown.
From the text:
And he had books, too; a tattered dictionary and a mauled copy of the California civil code for 19O5.