"unpleasant things like trip-wires and snares"

trip-wire is a wire that is stretched close to the ground so someone walking past will trip the device to which is it attached - the device is meant to detect or react to physical movement. Sometimes it is attached to a bomb, which will go off once someone “trips” the wire.

A snare is similar to a trip-wire, except that it is an anchored noose, and once tripped it pulls tightly around a leg or limb, restraining the victim. The video below combines a snare and a trip-wire.