What hints do you get to reveal that the animals expectations would not last long?

"They did not know when the Rebellion predicted by Major would take place, they had no reason for thinking that it would be within their own lifetime, but they saw clearly that it was their duty to prepare for it."

"Some of the animals talked of the duty of loyalty to Mr. Jones, whom they referred to as "Master," or made elementary remarks such as "Mr. Jones feeds us. If he were gone, we should starve to death."

"Why should we care what happens after we are dead?" or "If this Rebellion is to happen anyway, what difference does it make whether we work for it or not?"

"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."