I think "DEATH" must be the safety word they are using.
On to knots.
You and your sidekick are chasing a sexy villain across the roof tops. The cat-burglar is able to dash to the edge and gracefully jumps 20 stories to the distant ground. You boys are stuck and the vileness is taunting you with her stolen goods and gorgeous, criminal body. Sucks to be you, Batman. UNLESS you remember today's knot! The reef knot is used to tie two ends of line together. This is how it goes.
1) Pass the working end once around the other line.
2) Bring the ends up with the working end underthe other line.
3) Pass the working end over the other line.
4) Tighten by pulling both ropes on both sides simultaneously.
You now have a reef knot. If you tied this one with me, you can maybe see why it's often called a square knot. You can now use it to go down the side of a Gotham skyscraper. One note of warning: This knot is secure when the knot is pressed against something (like the side of a building). If, say, Catwoman had gotten to a distant building and Batman needed a longer rope to swing across on, he would not use this knot. He would use a different bend. We'll learn many more in the days to come.