Cut 4 even strips of wire
take 2 and begin to wrap them around each other
Use duck tape, hot glue or anything else to attach both of the combined strands together
Cut as many strips of wire as you want barbs. I tend to do atleast 6.
take the tiny peace of wire and wrap it around to get the barb look.
once you have done all of the barbs it should look like real barb wire. you can finish off the barb ends with red paint (blood!!!!!!) or clear finger nail polish to keep it from poking you.