Lennie grabbed a girl's dress in weed at the farm. Lennie and George had to run and hide in the river
Lennie wanted something soft to pet so George gives him a puppy. The puppy gets a little aggressive and Lennie gets scared and accidentally kills it
Lennie and Curly's wife were in the barn talking and Curly's wife let Lennie play with her hair. She got mad because Lennie was messing it up and started yelling and moving harshly. Lennie tried to control her but accidentally snapped her neck.
After Lennie realizes he had just killed Culy's wife, he runs away into the forest. Curley, Carlson, Slim and George go looking for him
George eventually finds Lennie in the forest hiding. George decides that if anyone should kill Lennie that it's himself. George puts a gun up to Lennie's head and shoots.
Carlson shoots the dog in the back of the head which foreshadows Lennie getting shot in the back of the head