A funkness device, or funkness cable, is a rock climbing tool used to remove jammed protection equipment from the rock. It consists of a simple steel cable about two or three feet long, with a swaged loop at each end.
What good is this thing? Well, say you're out trad climbing with your buddy, and he's leading the way up the rock. As he goes up, he will place protection gear (or "pro") into cracks in the rock, for safety in case of a fall. When you follow him up your job will be to "clean," or remove each piece of gear as you pass it, and take it with you for use later. But sometimes, a piece of pro will become fixed in place, and you'll find yourself unable to easily remove it from the rock. You could always abandon the gear and move on, but that piece you leave behind might be really necessary later in the climb.
That's where the funkness device comes in. Using a couple of carabiners, you clip one end of the cable to the stubborn piece of pro, and the other end to the eye of your climbing hammer. Then you swing the hammer forcefully away from the rock, as if hammering an invisible nail into the air behind you. This jerks the cable tight and puts a tremendous amount of force on the protection, hopefully yanking it free.
This operation does have a few disadvantages. Most seriously, there is a possibility of damaging the rock, which is against the ethics of the modern trad climber. There is a small risk of injury, as the gear will tend to pop out with significant velocity, and could hit you in the eye or some other sensitive area. Also, depending on how strongly the gear is wedged, you might destroy it before it comes loose.
Despite the downsides, the funkness device is still often worth carrying on your rack. It's cheap, not too heavy or bulky, and helps you avoid abandoning expensive climbing gear. Plus it has the coolest name of any sports equipment that exists.