Abandoned coal mines tell a story.
When you enter one of these derelict mines you often see these sections of trees that are referred to as timbers or props.
Instead, these timbers were used as a warning, “when the timbers start talkin, the miners start walkin”.
If a section of the roof began to sag, the wieght would press down on these timbers, they would begin cracking, popping, and sweating as the pressure squeezed the sap out.
When these warning signs were observed, the area was hopefully evacuated until the section of roof fell in a controlled or uncontrolled manner. Wedged at the top, tapered and set on the bottom, they were set very snug to prevent kicking out if pressure was applied.