狼 (láng): Wolf. In traditional Chinese culture, the wolf is a symbol of greed, ferocity, and untamed cruelty.
心 (xīn): Heart. Metaphorically, the heart is the center of one's conscience, empathy, and morality.
狗 (gǒu): Dog. While modern culture loves dogs as pets, in classical Chinese idioms, dogs often represent something base, lowly, or lacking dignity.
肺 (fèi): Lungs. In this context, lungs, like the heart, represent a person's inner essence and constitution.
The characters combine to create a powerful image: a person whose innermost being—their “heart and lungs”—is not human but is instead made of the cruel, savage parts of wild animals. This signifies a complete and horrifying lack of gratitude, morality, and human feeling.