Pterocarpus angolensis, or wild teak, looks like a perfectly normal tree until it’s wounded. When you cut into it, it dribbles long trails of dark red liquid down its trunk. For this reason, wild teak has come to be known as bloodwood.
This phenomenon is caused by tannin, a naturally occurring polyphenol found in plants, seed, bark, wood, leaves, and fruit skins. Regular plants typically contain about 12-20% tannin - wild teak sap contains about 77%.