The whisky incident refers to the first time the pigs sample alcohol. Orwell describes them in a sort-of blundering fashion; because the large amounts of alcohol they consumed has made them ill, the pigs begin to think they, and most importantly Comrade Napoleon, are dying. Orwell may have used humor here to give the reader a chance to laugh at the pigs, to show us that the pigs are not infallible even though they have taken control over the farm and consider themselves the "brain workers."
A key significance to this moment is that the next day the pigs, of course, change the commandment which originally banned the drinking of alcohol by animals so that it included the phrase "to excess" - another blatantly corrupt use of the pigs' power.
@Lit24 Is that 'the whisky incident'? Isn't there a scene where the pigs, who recently moved into the farmhouse, discover Jones's drinks cabinet and get very drunk and all have hangovers the next day and then, if memory serves, they make a new law banning alcohol?
In Ch.II of "Animal Farm" Mr.Jones the owner of the farm goes to Willingdon on a Saturday and gets drunk and returns to the farm only on Sunday afternoon and goes to sleep on the sofa. The animals had not been fed till now and by Sunday evening they begin to rebel. Mr.Jones and his men try to beat the animals to submission but to no avail. Soon the animals chase away Mr.Jones and his family and the workers from the farm. The farm is theirs and the rebellion had been successful.
In this scene Orwell mocks at the 1917 Russian Revolution when the workers and the peasants of Russsia overthrew the rule of Tsar NicholasII. This allegorical incident humourously reveals the indifferent attitude of the Russian aristocrats to the sufferings of the peasants.
Orwell adopts a humourous and light hearted tone so that his readers will enjoy his work of satire. If he had written about the injustices of the Russian king and the cruel mannner in which he treated the workers and peasants in a realistic manner the readers might have been repulsed by what he had written. The humour tones down the harshness of the situation and at the same time makes entertaining reading.