What is the importance of thresholds in the novel, Dinner at the Center of the Earth?

In the novel, Dinner at the Center of the Earth, thresholds serve as symbols for the crossing of boundaries. The world threshold implies a limit of safety; thus, when characters are described as being “at the threshold,” they are on the border between safety and danger. To cross a threshold is to surmount a boundary and perhaps put oneself in foreign territory, oftentimes that of an enemy.