Tree boles.
Those water filled hollows you see in trees in the woodland and forest every now and again.
They're like natural scrying mirrors or some kind of shimmering portal if you catch them in the right light. Ever so important for the survival of wildlife, many species of mammals frequent these spots with badgers and foxes being known to drink from them.
These water-filled tree holes, commonly referred to as tree boles or dendrotelmata,
(from the greek words for “tree” and “pond”) develop when water accumulates in cavities related to tree architecture or in rotten parts of the tree. These structures can occur in forest ecosystems and may represent essential microhabitats in the life cycle of various animal species.
Folklore here also tells of using this water for Witch bottles and for use with incantations to Ward your home. For those who don't know a Ward is a protective barrier made around yourself, your room, your home, or just about anything else. It can be physical or visualised.
The making of a Witch bottle sometimes involved putting rusty nails, pins and other disgusting things, like piss into a jar or bottle, to either protect or curse. The water from tree boles has also been known in folklore to have curative powers and it's said that water collected from the hollows in old beech trees was thought to be a cure for skin complaints such as eczema, warts and boils. Even the timing of when the water was gathered was important, being most potent under a full moon with a visible reflection. A water soaked piece of cloth would be wrapped against the affected part of the skin in the hope of cure. After a certain amount of time the cloth was then removed and then hung from the tree as an offering of thanks. Probably where a part of the Cloutie (clootie) tradition may have originated from perhaps.
So take a look the next time you're out and about and have a closer look for a tree bole.