Military applications of Silly String:

I'm a former Marine I in Afghanistan. Silly string has served me well in Combat especially in looking for I.A.Ds., simply put, booby traps. When you spray the silly sting in dark areas, especially when you doing house to house fighting. On many occasions the silly string has saved me and my men's lives...

When you spray the string it just spreads everywhere and when it sets it lays right on the wire. Even in a dark room the string stands out revealing the trip wire.

(Via Boing Boing.)