1. why do we want to write a clever title?

Writhing a great title helps the reader get a hint of what a book will be about. With a catchy title a person would show intrest in your essay or book or whatever it is you are writing.

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.