Which detail does Orwell include to support the theme that dictators care only about themselves and not those they
rule?
"Napoleon himself appeared at the meeting on the
following Sunday morning and pronounced a short
oration in Boxer's honour."

"It had not been possible, he said, to bring back their
lamented comrade's remains for interment on the farm,
but he had ordered a large wreath to be made from the
laurels in the farmhouse garden and sent down to be
placed on Boxer's grave."

"And in a few days' time the pigs intended to hold a
memorial banquet in Boxer's honour."

"Napoleon ended his speech with a reminder of Boxer's
two favourite maxims, 'I will work harder' and 'Comrade
Napoleon is always right maxims, he said, which every
animal would do well to adopt as his own."

The details Orwell includes to support the theme that dictators care only about themselves and not about those they rule is:

"Napoleon ended his speech with a reminder of Boxer's  two favourite maxims, 'I will work harder' and 'Comrade  Napoleon is always right maxims, he said, which every  animal would do well to adopt as his own."

Explanation:

Napoleon and Boxer are characters in the allegorical novella "Animal Farm", by George Orwell. The novella is a criticism to the Soviet regime in Russia. The pig Napoleon functions as a representation of Joseph Stalin. Napoleon does not care about the other animals in the farm. All he wants is for them to work while he lives comfortably. The most hard-working of all is a horse, Boxer, who is already eleven years old. When Boxer can no longer perform, instead of retiring him and supporting him for the rest of his life as he had once promised, Napoleon sells him to a slaughterhouse.

Still, at Boxer's funeral, Napoleon pretends to care about Boxer. The animals are unable to see through this façade, but it is all crystal clear for readers. Orwell even includes the ironic detail of Napoleon telling the animals to adopt Boxer's maxims as their own. Every animal, according to him, should think of Napoleon as incorruptible, as the perfect leader, and every animal should also work harder. Napoleon did not care about Boxer and he does not care for the ones who are still alive. All he wants is for them to keep on working, ignorant of his immoral behavior.

type of error:

the error in the sentence is a "dangling modifier". a dangling modifier is a phrase, word or clause that "dangles" because there is not target to modify. in this case, "after mopping the floor" is the dangling modifier since it has no word to modify. the noun "house" cannot mop the floor; therefore there is a mistake in the writing of the sentence.

in our power to make a world happy - to teach mankind the art of being so - to a character hitherto unknown - and to have, as it were, a new creation intrusted to our hands, are honors that command reflection, and can neither be too highly estimated,