When using the perfect tenses of verbs, it's necessary to add a/an

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.

- "he is a very real person and his intent isn't to influence us vonnegut addresses this towards the end of the letter when he says, if we choose to curse, that is by our own individual means."

the words “strangest” and “unusual” suggest that the narrator is about to tell the story of an odd or puzzling group of people.