What causes Framton’s sudden departure? What explanation does Vera offer?

Nuttel's departure that was so sudden it was if he had seen a ghost. The three hunters coming terrifies him. Vera says that she believes it was the spaniel that frightened him; she tells her aunt and uncle that Nuttel is terrified of dogs ever since being hunted into a cemetery in India by wild dogs and having to spend the night in a newly dug grave.