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
The sea gave no particular reply. So the squirrel mother started to dry the ocean by soaking her tail in the sea and letting the water drip off on dry land - again and again. Little did she consider that the water would seep and run down into the sea again. But the sea got so alarmed by the squirrel's determination that it swelled up a huge wave where the cubs were floating, and put them all beside her on the brink - and lo, they were all alive and well again, after being drowned and gone for many days.
Yogananda with squirrel 1924