Actually, it's no big deal. Dr. Yuan is just being overly cautious because this blood clot is morphologically completely different from any previous clots, so he feels uncertain.
If it weren't for the unusual nature of this clot, Dr. Yuan would have concluded much earlier. It is precisely this clot that keeps Dr. Yuan from reaching a conclusion.
He called his mentor for advice, and the mentor mentioned having seen such cases before, suggesting consulting clinical experts. Clinical experts have a deeper understanding of the pathophysiology, pathology, anatomy, etc., of pulmonary embolism than forensic scientists; their medical knowledge far exceeds that of forensic scientists.
