What is Lennie doing in the barn by himself?

From the text:

Only Lennie was in the barn, and Lennie sat in the hay beside a packing case under a manger in the end of the barn that had not been filled with hay. Lennie sat in the hay and looked at a little dead puppy that lay in front of him. Lennie looked at it for a long time, and then he put out his huge hand and stroked it, stroked it clear from one end to the other.