How does the tone of the doctor and the squire’s conversation change after Dance leaves? Why?

In the closing of Chapter Six, the tone becomes a bit ominous, as Dr. Livesey notes the danger of their plan, and after the Squire leaves, he concedes that the primary danger will be found in the Squire's lack of discretion.

The tone of the conversation between the doctor an d the squire gets more serious after Dance leaves. The conversation is almost business-like. Both characters probably realize that this is serious and important. They also get really excited when they realize the significance of the map.