All of them came to look at Snowball's drawings at least once a day. Even the hens and ducks came, and were at pains not to tread on the chalk marks. Only Napoleon held aloof. He had declared himself against the windmill from the start. One day, however, he arrived unexpectedly to examine the plans. He walked heavily round the shed, looked closely at every detail of the plans and snuffed at them once or twice, then stood for a little while contemplating them out of the corner of his eye; then suddenly he lifted his leg, urinated over the plans, and walked out without uttering a word. –Animal Farm,
George Orwell

Which statement best suggests a cause of the conflict between Napoleon and Snowball?