A 58-year-old woman is discovered in her burnt kitchen in Mumbai. The body shows severe charring with blistering of the skin in multiple areas. Soot is present in the trachea and bronchi. The lungs show a cherry-red discoloration. Carboxyhemoglobin level is 48%. There is evidence of thermal injury to the larynx and tracheal mucosa. The pathologist concludes this is an ante-mortem burn. Which of the following findings was MOST critical in reaching this conclusion?