Caiman: His Body as Evidence
A medical examination in Volume 2 turns Caiman’s search for his past toward evidence he cannot interpret alone.
Spoilers throughout. This page assumes you have finished the series.
Caiman's missing past makes his own body a source of evidence he cannot interpret alone. His decision to take his severed head to a doctor in Dorohedoro Volume 2 turns the search for an identity into a practical investigation.
A suspect is not the only possible lead
VIZ's first-volume description establishes the initial approach: Caiman and Nikaido hunt sorcerers in the hope of undoing the transformation that left him with a reptilian head and amnesia. That approach makes another person's identity the immediate problem. Finding whoever caused the change seems to offer a route back to Caiman's own.
The doctor's examination changes the direction of that inquiry. Carlo Santos's Anime News Network review of Volume 2 records Caiman carrying the remains of his severed head and then deciding to have a doctor examine them. The remains become something to investigate. They are no longer merely evidence that someone has injured him.
The person asking is also the evidence
My reading is that this decision gives the identity mystery a useful discomfort: being Caiman does not make him the best interpreter of Caiman. He possesses the object under examination without possessing an explanation for it. That is a more precise problem than a general wish to discover himself. He needs knowledge that his own experience cannot supply.
Seeking an examination also changes what counts as action. An attack can force an encounter, but it cannot by itself make an unfamiliar body intelligible. Bringing the head to a doctor makes room for another kind of competence. The choice matters even without treating it as a complete change in Caiman's behavior or a successful solution to the mystery.
There is a limit to this reading. Asking how the head works does not answer which memories belong to him, which account of his past is reliable, or how he should treat other people. Physical evidence can help establish an origin; it cannot make every decision that follows from learning it. The useful distinction is between finding a cause and deciding what that cause means for the person who has to live with it.
This study concerns the investigation in Volume 2, not the eventual explanation of Caiman's identity. For a separate discussion of identity and a changed body, see the Alphonse Elric character study.