What does the snake in the bamboo tube mean? What is the explanation?

(1) As the saying goes, a curved snake naturally straightens when it enters the bamboo tube. Metaphor into meditation, its heart naturally straight. It is synonymous with the phrase "snake into the bucket to change songs" in teacher Lunga's notes. Great Wisdom Volume 23 (Big Two Five? Back to 234): "It is the heart that has no beginning since the world, and it is often crooked, so it is correct and straightforward; For example, snakes often bend, but when they enter the bamboo tube, they are straight. 」