Here's why:
* Physical Appearance: Lennie is described as being big and strong, similar to a large dog breed. He is also clumsy and has trouble controlling his strength, like a puppy.
* Loyalty and Affection: Lennie is incredibly loyal to George and has a strong desire to please him. He sees George as his protector and leader, much like a dog would see its owner.
* Simplicity and Childlike Nature: Lennie's mental capacity is limited, making him innocent and childlike in his understanding of the world. This innocence is often associated with dogs.
* Desire for Companionship: Lennie craves companionship and affection, much like a dog longs for its owner's love and attention.
While the comparison to a dog is a prevalent one, you could also argue that Lennie could be seen as a bear due to his size, strength, and sometimes clumsy nature.
Ultimately, the animal Lennie represents depends on the specific aspects of his character that you want to emphasize.