What does Ix-Nay mean when he tells Tully that there is a rabbit in the moon when they are in Belize?

As Tully and Ix-Nay walk toward the landing strip in Belize the night after watching The Man Who Would Be King, Ix-Nay tells Tully that there is a rabbit in the moon. He explains that the shadows on the moon are a sign that something big is going to happen, like a new friendship.