Without more context about the specific piece of writing, I can offer a general interpretation. It seems like the author includes the detail about the lady being quiet when the number reaches ten to highlight a shift in the conversation or mood. The silence may indicate a moment of reflection, uncertainty, or perhaps discomfort with discussing a particular topic related to how things used to be on Terra. It could also suggest that the topic becomes more complex or significant at that point, prompting the lady to pause and consider her words carefully. Overall, the author may use this detail to add depth to the character's portrayal and to emphasize the importance of the conversation or theme being discussed.