What are is the significance of these lines from shakespeare?

Who gave you these questions? The speaker is telling the protagonist to watch out for jealousy, not suggesting revenge. There is just the bare mention of jealousy as a monster, which hardly counts as an image (suppose Shakey could have made it a dragon, that wd be different). The flaw, if any, would be acting on the jealousy, or being consumed by it. A cuckoo lays its eggs in other birds' nests, therefore the other bird is cuckolded. If a man is cuckolded, his wife has been with another man. There is no strong animal imagery here. And I fail to see any dichotomy here between appearance and reality. Sorry I couldn't help you, but the questions don't make sense.