How does the author foreshadow the pigs' decision not to share the milk with the rest of the animals?

Orwell foreshadows Napoleon's confication of the milk when Napoleon distracts the other animals from the topic by telling them not to worry about it. He took care of it alright.

"Never mind the milk, comrades!" cried Napoleon, placing himself in front of the buckets. "That will be attended to. The harvest is more important.
Comrade Snowball will lead the way. I shall follow in a few minutes. Forward, comrades! The hay is waiting."

So the animals trooped down to the hayfield to begin the harvest, and when they came back in the evening it was noticed that the milk had disappeared.