"He had gone out alone to drag a load of stone down to the windmill"
"It is my lung, said Boxer in a weak voice.
"Boxer! she cried, how are you?"
"Fools! Fools! Fools! Do you not see what is written on the side of that van?"
Alfred Simmons, Horse Slaughterer and Glue Boiler, Willingdon
At this point in the scene Boxer went out to go drag some stone towards the windmill by himself.
"Boxer! Boxer! Get out! Get out quickly! They're taking you to your death!
At this point in the scene Clover finds that Boxer is ill and it has something to do with his lung and he can't get up.
"It was the most affecting sight I have ever seen! I was bedside at the very last. And at the end, almost too weak to speak he whispered in my ear that his sole sorrow was to have passed on before the windmill was finished. Forward comrades!
At this point in the scene a man comes and takes Boxer, Benjamin realizes this and tells the other animals to look what it says on the side of his van.
Didn't the side of the van say "horse slaughterer"?
I think it did, how could Squealer make such a stupid mistake?
During this part of the scene Clover and the rest of the animals are trying to tell Boxer to get out of the van but Boxer is too weak to try and get out of the van.
During this point in the scene Squealer had told some of the animals that he was with Boxer when he died at the hospital, which wasn't what actually had happened.
During this part of the scene some of the animals had remembered that the van on the side had said "Horse Slaughterer" and the animals began to think that Squealer made a mistake. (the quotes aren't direct they are inferred as to what the animals would have said.)