I just so happend to be replacing a string on an acoustic guitar as it had torn appart (it was a bit old). Once I had removed it, I noticed it looked kinda cool and I could use it for something on my 40K models.
To explain, its a 4th string wire for a nylon string guitar (just ask anyone at a music shop about it, they will explain). Essentially, there are 2 parts to the wire, a string part (not sure if its a bunch of nylon strands, looks like cotton string) that is wrapped in a very thin brass wire. The effect I saw was when the central string had torn, leaving only the brass wire intact. Once I removed the whole lot from the guitar, I noticed that if I pulled the brass wire, it unfurled from the central string and had tiny ridges all the way along the brass wire. It looked amazingly like tiny barbed wire. After test wrapping it around a pencil, I let it go and it looked great. I unwound the whole brass wire, wrapped it around a pencil tightly and then when I let it go, I cut up the coil into sections. They’ll eventually go on my model bases as torn up barbed wire.
Here is what it looks like on my bench top: