When Mr. Whymper visited from the outside world, how did Napoleon hide the declining state of Animal Farm from him?

Napoleon hid the declining state of Animal Farm from Mr. Whymper by doing the following:

1) Selected animals, mostly sheep, are tasked to remarked casually about the increase in food rations if Mr. Whymper is around to hear their remarks.

2) Napoleon ordered that the near empty bins in the store-shed be filled with sand until it reaches the brim and top it with the remaining meal and grain. Mr. Whymper will then be guided into a path which will enable him to see the filled bins.