Why was Lennie mad at the puppy?

Lennie, from John Steinbeck's "Of Mice and Men," was not mad at the puppy. He was actually extremely fond of the puppy and treated it with great care and affection.

However, Lennie's lack of understanding of his own strength led to him accidentally killing the puppy by petting it too hard. This caused Lennie great sadness and guilt, as he truly loved the puppy.

The incident highlights Lennie's mental disability and his inability to grasp the consequences of his actions. It also serves as a foreshadowing of the tragedy that will unfold later in the story.