If you've read the warning, then now you are in spoiler territory. Don't say I didn't warn you.
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At the end of the hospital level, Mono leads the Doctor inside of a crematory, where he is able to craw out through the bottom and trap the Doctor inside when Six closes the door to the crematory shut. Now, it's here that you have two options to decide the Doctor's fate: either you can leave him trapped inside of the crematory, or, you can turn on the crematory and burn the Doctor alive. The smell of his burning flesh rises, as he slowly screams and begs and cries during the process.

A lot of people on Youtube that I've seen almost always choose to turn on the crematory and burn the Doctor alive. I'm not sure if people knew if there was an option to spare him, but believe it or not, there is. If you do, you get the achievement, "First do no harm". You might think you're offering him mercy, but if you read the description of this achievement, you get these words:

It's crueler to let him live.

Now THAT is dark. You don't just say that after sparing someone's life. CJ, how exactly is this option worse? I'm pretty sure getting burned alive is worse than dying of starvation or dehydration.

To that I say, never underestimate starvation or dehydration.

"Depriving the body of water has fascinating effects. With no fluids coming in to filter, the kidneys shut down, and your body starts poisoning itself, making you sicker and sicker. Once those poisons have time to build up, you can suffer a total organ failure, or a heart attack, or a stroke!"

"Starvation is another classic, too, but that's really a SLOW moving train. It takes weeks for the body to use up its stores of nutrients and break down all of its proteins, and turn on itself. It can take weeks! Some people have even lasted a couple of months!" - Funtime Freddy, Count The Ways