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.
Although most rescue gear is commercially manufactured, knots are "manufactured" by rescuers during the mission. It is critical that rescuers know how to tie knots properly and quickly.
"Dressing" a knot refers to the process of adjusting the individual strands of rope so each one is in the proper place and doesn't have any unnecessary twists or slack. Dressed knots are stronger and much easier to inspect.
After tying a knot, it is important to consider the length of the tail(s) exiting the knot. Although some knots require a backup knot to prevent them from untying (notably the bowline), most rescue knots are safe with an unsecured tail that is three or four inches long (about "fist-width").
Adding a knot to a rope weakens it significantly. The decrease in strength varies by the type of knot, but a good rule of thumb is that knots weaken rope by 33d and webbing by 45%.
Adding additional knots does not further weaken the rope. For example, adding six more knots to a rope that already has one knot doesn't weaken the rope.
One way to become proficient at knots is to limit your selection to a handful of versatile knots. Here are some of the most popular rescue knots.
Here are a few more knots that are handy to know.