Occasionally we find unwelcome hidden objects in the timber
This is a plank of American Black Walnut from North America, we can only assume that it was shot by a hunter who missed his target, embedding his bullet into a tree rather than the intended animal, possibly a lucky escape for it.
Sometimes these hidden objects can cause us problems when cutting, planing or routing as they can jam or blunt our cutters. We often find lead shot in English timbers but the worse culprits tend to be nails or staples used to fix fencing or barbed wire to trees dividing fields or boundries, these can become overgrown and embed themselves into the trunk. We do thoroughly inspect our timbers before cutting or machining for such nasties. They can't always hide that easily though, as iron trapped in Oak for instance does tend to leave a tell tale blueish grey stain.