Zombification?

Dean pushed the Zombie aside, immediately rolled over, and checked the wound on his left shoulder. His armor was cracked open and his shoulder had been bitten badly. If it were someone else, it would have been too painful to say a word. But his left hand was numb. It made him feel weird, like looking at someone else's wound.

His left hand could only hurt others, and he himself would not feel any pain. However, this was only an illusion.

Dean turned his head, pulled out the dagger from the Zombie's eye, and returned to the subway. He wiped the blood off the dagger with a towel, washed it with clean water, and then burned it with the torch. When the dagger turned red, he took off his armor and used the hot dagger to scrape the wound on his shoulder. There were hissing sounds coming from the wound.

After the mangled flesh was scraped, Dean suddenly discovered that there was no blood flowing from the wound.