Instinct

Stanley saw the corpse of the young man in front of him and immediately felt like throwing up. He had seen corpses before. He had seen one just minutes ago.

Even so, he had never felt like vomiting at the sight of any of them like he was right there.

The sight of the young man with the side of his head crushed in and unnatural fluids flowing out of that hole caused Stanley to feel incredibly queasy. 

He closed his eyes, moving the man he was helping to the side so he didn't see it as well. He took a moment to gather himself and took a deep breath before turning back around.

He looked carefully at who it was that had died, and Stanley recognized the person. 

Marcus.

Marcus was from Stanley's own batch. He was one of the people that never held back against Stanley during their fight, due to the fact that he considered Stanley a Dull.