If you're into rappeling or knot tying for fun or practical survival, have a look at this Bachmann knot. You're going to need it if you're going to encounter climbing up a wet rope. For those not familiar with it, the Bachmann knot is a uni-directional, meaning it can only be loaded from one direction and that's down. Again, its something that most survivalist should know, but how many have actually practice climbing with it? See the video here.