In The English Patient by Michael Ondaatje, what do Caravaggio's cut thumbs mean?

David Caravaggio, a Canadian who knew Hana and acted as an "uncle" towards her before the war, is in Italy as an Allied spy. His hands are bandaged, but one day Hana takes the bandages off. Caravaggio tells her that the Germans discovered he was a spy. He says that in retaliation, his wrists were handcuffed to table legs and his thumbs cut off. The removal of his thumbs was painful and traumatic: "When they cut off my thumbs my hands slipped out of them without any power."

The novel says that "history enters us." One of the themes is that history has a physicality that we carry with us. The English patient is burned; Caravaggio has lost his thumbs. "He turns one hand over ...what looks like a gill is where the thumb has been cut away." The lost thumbs are a physical marker of what the war takes from people. Having hands (not being on four legs) and separate thumbs is part of what makes us human. We don't have "gills." The loss of the thumbs reflects the dehumanizing effects of the war.

The cut thumbs symbolize the way that World War II has scarred and harmed Caravaggio. Like Hanna, he is one of the war's victims. He will no longer be easily able to take up his former trade as a thief because of his lost thumbs. He identifies himself not by his name but by his army serial number. He takes morphine to deal with his pain. The loss of his thumbs has reduced his humanity. The war has both physically and emotionally damaged him.