Brent's cause of death was carbon monoxide poisoning, but when Lucy identifies his body, she comments that he looks "like a smurf," indicating a blue tint to his skin, which the coroner says is a by product of dying in an oxygen-poor environment. However, carbon monoxide kills you by combining with the hemoglobin in your blood more readily than oxygen, and in doing so turns a very bright red. Therefore, people who die from it typically have a very bright, almost cartoonish, pink tint to their skin, not a blue one.