after Percy overhears the conversation between Grover and Mr. Brunner, how does he feel? what is he suspicious of?

Even though he feels a bit guilty, Percy can't help eavesdropping. In the conversation, he hears that Grover is worried about him being alone during the summer. Apparently, in both Grover and Mr. Brunner's eyes, the discovery of a 'Kindly One' at school is a worrisome development.

Explanation:

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.