On the Edge
This pun is used well to summarize the events in the chapter because of its two meanings. The first meaning is that Joe and Simon are literally on an edge, that they are on a ridge line. The second meaning is that Joe and Simon are near the end of their abilities, strength and supplies, they are close to losing control and potentially die, or fall of the edge. This summarize the chapter well because throughout the chapter the come closer and closer to losing control, they have multiple falls and sketchy moments that they barely make it through.
The use of symbols to represent ideas or qualities. The gas stove running out of fuel symbolism that Joe and Simon are running out of time and energy. It shows us Simon and Joe are moving closer and closer towards failure, accident, or maybe death.