That was a farmer who was attacked by a Slime in the wild; he accidentally stepped on a Slime in a pit, resulting in the corrosion of the skin on half of his leg.
Slime attacks are very weak, generally weaker than Goblins, and they are considered gentle Magic Creatures.
However, even the weakest Magic Creature will counterattack when stepped on.
When the injured farmer was brought in, although there was no life-threatening danger, the skin on his entire lower leg had melted away, revealing large patches of blood-red flesh, a terrifying sight, leaving him barely enough energy to scream.
However, such injuries, though startling, are not actually severe; otherwise, he would have been taken to the Church to see Clerics and Bishops immediately.
Over the past few days, the Hero had been interning at the Medical Care facility, learning how to use Healer skills.