Final answer:
The phrase 'upper hand' refers to a dominant position or advantage in a situation, not a physical stance.
Step-by-step explanation:
The phrase "upper hand" generally refers to a dominant position or advantage in a situation. It implies having control or an advantage over another party. In a historical context, like uncovering Union secrets during the American Civil War, having the 'upper hand' would mean having the strategic advantage that could affect the outcome of dealings or conflicts. This phrase is not related to a physical stance or position of the body, which seems to be described by the other options provided in the question which are not relevant to the phrase 'upper hand'.