The Thing Cheats

Highlight ''Flare'' and enable it but don't throw it. When it is low, press Left or Right and highlight another object. Then, highlight ''Flare'' again. It will have restarted and you will not lose another one.

When standing in the warehouse just outside from where the second Thing boss lurks, you will notice a garage door to the left of the Boss's door. Get an ally to stand near the garage door, then back up and throw a grenade at them. If done properly, you can cause the character to run towards the door and it will open. Run inside before it shuts and watch the video.