Foods
Aside from the endless supplies of teas, all of my books have a focus on food prep, cooking food, serving food, and eating food. That is not an accident or due to my own obsession. Our understanding of culture is often wrapped up in food and customs around food. Think of how we put ethnic labels on food and identify groups of people with certain foods.
One of the things that make the dragons feel so alien is they eat their food raw, no ceremony and no sharing except providing for youngsters. That is a jolt to most readers and then as you dig deeper and meet the dragons of the Combined Territories you see their embrace of food and the culture of hospitality and sharing food.
As the story thrives and expands it includes other cultural differences, some leaning more heavily on the dragons, some on the humans. What do you think is the most startling difference?