Zen emphasizes experiential wisdom in the attainment of enlightenment. Like the Bodhidarma, squirrels come to teach a special transmision outside of scriptures... not founded on words or letters. Through the Zen of Bucky Squirrel, wisdom is passed through the one-to-one direct transmission or experience... squirrel to human. Such lineage continued all the way from the Buddha's time to the present.
The existence of bodhi squirrels was substantiated by the late Paramahansa Yogananda. He told the story below, which I found in Avatar Animals and Yogananda~ http://oaks.nvg.org/ouav.html
Yogananda with squirrel 1924