Arborist knots keep a climber secure high off the ground and control the limbs coming down. Top friction hitches like the Blake's Hitch, Distel Hitch, and Prusik grip the line under a climber's weight but advance by hand when unloaded, so the climber can move up, stop to work, and come back down. Rigging systems are another aspect of the arborist's job. A rigging knot like the Timber Hitch grabs the log or limb and ties it to the rigging line. It holds the load. It doesn't lower it, and nothing should be let down on it without a proper, backed-up rigging system. The lowering runs on friction instead, where a knot like the Munter Hitch on a carabiner feeds a cut section down under control rather than dropping it. An Alpine Butterfly forms a solid loop in the middle of the line for an anchor or attachment point. Tree work can be extremely dangerous, and a mistake can kill, so arborists practice these essential knots until tying, dressing, and checking them is second nature.