The unique personality of that one specific dog mentioned in "Darkness" is that when the owner dies, he tries to protect his corpse, rather than eat it.
Nick calls Tom and Daisy “careless people” because he recognizes them as selfish, insensitive individuals who take advantage of people and retreat back into their money without accepting responsibility for their actions. After spending time with the Buchanans, Nick is appalled by their lifestyle and reckless decisions.
The fable starts with the city mouse inviting the country mouse over. The country mouse agrees and travels with the other mouse back to the city. The city mouse shows all the food and luxury he has in his home such as flour and oatmeal. Both mice then are force to hide from people who are considered dangers. The country mouse chooses to Leave because he'd rather live with little resources than to live in constant danger.