Book 16: Splitting of horses. The two horses splitting is a symbol for Zeus and his son, Sarpedon, separating. Despite Zeus wanting to save his son, he is unable. Thus, the two are separated just as the horses.
Book 17: Burning of the ship. The ships were the only way home for the Acheans. When they burn the first, it symbolizes that this is a crucial moment.
Book 18: The shield of Achilles. It depicts the fact that war is part of every day life. Children hold hands and dance in a circle, young men holding knives in their hands. Also, a scene of bulls being herded by dogs and lions. This inspires hope to Acheans, there are few lions just like the small numbers of them, yet the few lions are able to take on the bulls.