That's just an iv bruise. Could be anything.

The infestation is beginning to leak.

Thin skin bruises easily.

That's what happens when you're soul has decayed so far past dead that the necrotic void that has replaced it has expanded to the point of physiological manifestation. Once the saturation hits 100% he'll collapse into a micro-singularity and near instantaneously evaporate. The resulting radiation burst will be enough to give 1st degree burns to anyone standing within 10 meters.