A critical subject or situation with concealed or unpredictable implications.
A piece of exercise device consisting of a pivoting tube attached to the ground to which a barbell can be fitted to lift it off the ground.
A mine that is placed on land and designed to explode when stepped upon or touched.
A potential, unsuspected, hidden problem, hazard, or danger that is easily encountered but not immediately obvious.
A type of trap consisting of a concealed pit in the ground, which the victim is supposed to fall into and not be able to get out from.
An antipattern.
Subsidence below ground in a mine, which can cause the ground level above to drop.