The "critical point test" (aka "scissors test") requires that if any one item fails, nobody should be injured.
A "bend" is a knot that joins two ropes.
A "hitch" is a type of knot that must be tied around another object.
The "whistle test" requires that if all rescuers let go, nobody should be injured.
As with all "bends," the fisherman's bend joins the ends of two ropes. An advantage of the fisherman's bend is that it is relatively small. The potential downside is they are very difficult to untie after holding a heavy load. Because of this, the fisherman's bend is primarily used to join ropes that will not need to be untied (e.g., to create Prusik loops).
When this bend is tied using overhand knots, it is simply called a fisherman's bend. When the individual knots are tied with two wraps (as shown below), the individual knots are called double fisherman's knots and the resulting bend is called a double fisherman's bend. The knots can also be tied with three wraps (i.e., triple fisherman's knots).
This illustration shows the steps to tie a double fisherman's bend.
A double fisherman's knot can also be used to create a stopper knot near the end of a rope.