How does Lennie react to what he has done about killing Scully's life?

Yes.Not on purpose. Because Lennie is mentally challenged.Also he likes to pet soft things.He is mourning his puppys death. By shaking her so much that her neck broke off her body(remember Lennies a strong man).

Thanks to John Steinbeck and answer.com(I hope this helped)

By Podolski(podolsker),now nicknamed Lennie.