Answer: Silly String

While your recollection of Silly String might, well, call to mind silly things like pretending to be Spider Man and shooting string webbing from your hands, there’s a deadly serious application for the otherwise silly novelty spray.

Silly String is an expanding foam that, when sprayed through the tiny nozzle found on the can, turns into long string-like strands of foam that quickly sets in the air (due to the rapid evaporation of the solvents and propellants). The end product, a thin noodle of foam millimeters across, is incredibly lightweight–Silly String piled high on your hand barely weighs more than air. The extreme lightness of the product is exactly why U.S. soldiers began using it in the field.

The spray projects yards from the nozzle, it takes shape almost instantly, and it can drape across tripwires without triggering whatever trap the wire is attached to, allowing soldiers to either avoid or disarm the trap.