When the farmer bores the tap hole into the trunk, the tree sends sap to heal the wound. Sure enough, by the next spring, only an extremely observant and knowledgeable person can find the old tap scars. When the wind blows, the tree senses that a branch might break. A broken branch is a much more serious wound than a little clean tap hole in the trunk. Therefore, the tree withholds the sap from the tap hole in case it needs to rush a bunch of sap to a broken limb somewhere. Once the wind subsides, the sap starts flowing again through the little tap hole. Sentient beings, anyone? You bet. Fearfully and wonderfully made.
Joel Salatin The Marvelous Pigness of Pigs: Respecting and Caring for All God's Creation