A Monkey Fist is a ball bearing with para-cord tied around it. They are used for key chains. The cord can also be wrapped around your wrist.
In addition to being used as a make shift weapon and/or keychain; they are also used to cast lines, think nautical. The round weighted monkey fish with small diameter line in tow is cast from ship to shore or, ship to ship first; and then the lager, heavier lines are pulled across using the lighter line. Some friends of mine and I have used this for years with great success - works great for none maritime uses as well - like climbing buildings, trees, etc... Much, much easier to sling some paracord with a monkey fist at the end than a 3/8" or bigger line.