I'm just going on memory, but I think the proper name is Japanese Giant Hornet.

Wow, you have some difficult questions, haha. I'll try my best. The speaker is describing the terrible treatment he has received from the people in this community. He is overwhelmed by the cruelty of their words, and he says the phrase "Imagine saying any such things to a human person." This sentence sounds like a request or command as if the speaker is telling his friend to actually imagine it, but really it's just a more forceful and emotional way of saying "Can you imagine saying any such things to a human person?" So you are correct that the speaker is basically asking “Would you say any such things to a human person”? The response to that question is "No." Because the listener agrees with the speaker's point which is: It's unimaginable that one human being would speak to another human being in this way! By saying "No, you're right", the listener is literally saying "Yes, I agree with you. These people are doing the unimaginable by speaking to us like this"

I hope I can explain this. I believe this is the context: The characters in this passage are having a conversation about the people in their community/neighborhood. The characters here are describing the people in the community as being rude/hateful/cruel. Even though the speaker is angry, he admits that one of his neighbors demonstrated politeness. The phrase "I'll give him/her that" is basically stating that you are reluctantly/grudgingly acknowledging someone else. In this case, I interpret the speaker's words as: The people in this area are mean! But... I will admit that my neighbor did show me some kindness. (By sending me a note and using the word "please".) I hope my explanation made sense. Let me know if you'd like me to elaborate on anything.