Once again the animals were conscious of a vague uneasiness. Never to have any dealings with human beings, never to engage in trade, never to make use of money – had not these been among the earliest resolutions passed at the first triumphant meeting when Jones was expelled? All the animals remembered or at least they thought that they remembered it.

George Orwell

Animal Farm. Chapter 6. The reason for the animals’ unease is they are now trading produce with untrusthworthy humans, and using a solicitor as agent.