Unlike the above answer, I thought the question referred to the animals' celebration of their "victory" in the Battle of the Windmill. I'm answering on that basis.
The animals fire a gun and conduct a funeral procession, complete with more firing of the gun, speeches and songs.
It is, of course, ironic that the animals celebrate with human rituals. But what's really ironic in this episode is the fact that the animals are celebrating at all.
They say they've won a victory, but in truth, they've lost. The windmill they worked so hard to build is gone.
So what's really important here is that this is further proof of how Napoleon bends the truth to keep control of the farm.
In Ch.2 Mr. and Mrs. Jones along with the others are chased out of the farm by the animals. The rebellion by the animals had been successful: "Jones was expelled, and the Manor Farm was theirs." The animals celebrated their victory in the following manner:
1. The animals ran a victory lap all round the farm, just like an athlete after he has won a race or the members of a football team after they have won a match:
"Their first act was to gallop in a body right round the
boundaries of the farm."
2. Human beings usually celebrate a victory with a feast. After the animals had chased out all the human beings from the farm and had made a bonfire of "everything that reminded them of Mr. Jones," they had a sumptuous feast served to them by Napoleon:
"Napoleon then led them back to the store-shed and
served out a double ration of corn to everybody, with two biscuits for each dog."