A tripwire is a passive triggering mechanism. Typically, a wire or cord is attached to some device for detecting or reacting to physical movement. A tripwire may be a wire attached to one or more mines — normally bounding mines and the fragmentation type — in order to increase their activation area.. Alternatively, tripwires are frequently used in boobytraps, whereby a tug on the wire (or release of tension on it) will detonate the explosives. Soldiers sometimes detect the presence of tripwires by spraying the area with Silly String. It will settle to the ground in areas where there are no wires; if there are any, the string will be suspended in the air but not set them off due to its light weight. It was used by U.S. troops in Iraq for this purpose.