person who activates its trigger, or employed to reveal the location of an enemy by setting off a signalling device. Most, but not all, military booby traps involve explosives. There is no clear division between a booby trap and buried conventional land mines triggered by a tripwire or directional mine. Other, similar devices include spring-guns and mechanisms such as the SM-70 directional antipersonnel mine. What distinguishes a booby trap is that its activation is intended to be unexpected to its victim. Thus booby trap design is widely varied, with traps or their trigger mechanisms often hidden. Frequently at least part of the device is improvised from standard ordnance, such as an artillery shell, grenade, or high explosive. However, some mines have features specifically designed for incorporation into booby traps and armies have been equipped with a variety of mass-produced triggering mechanisms intended to be employed in booby traps deployment. Part of the skill in placing booby traps lies in exploiting natural human behaviors such as habit, self-preservation, curiosity or acquisitiveness. A common trick is to provide victims with a simple solution to a problem, for example, leaving only one door open in an otherwise secure building, thereby luring them straight toward the firing mechanism. An example that exploits an instinct for self-preservation was used in the Vietnam War. Spikes known as punji sticks were hidden in grassy areas. When fired upon soldiers instinctively sought to take cover by throwing themselves down on the ground, impaling themselves on the spikes. Attractive or interesting objects are frequently used as bait. For example, troops could leave behind empty beer bottles and a sealed wooden packing case with "Scotch Whisky" marked on it before leaving an area. The rubble-filled packing case might be resting on top of an M5 or M142 firing device, connected to some blocks of TNT or to some C4 explosive stuffed into the empty fuze pocket of a mortar shell. Alternatively, the weight of the packing case might simply be holding down the arming lever of an RGD-5 grenade with a zero-delay fuze fitted and the pin removed. Either way, when the case is moved, the booby trap detonates, killing or severely injuring anyone in the immediate area. Many different types of bait object can be used. For example, soldiers may be tempted to kick a beer can lying on the ground as they walk past it. However the can,