The thing controls our bodies like puppets, but it leaves us some part of our minds. Otherwise it could not feed off our feelings and emotions. So it leaves us the revulsion, the terror, the madness, and the pain. Always the pain. Always that great red hot sheet of blinding pain.
Every wound hurts.
And the awful thing sucks it in greedily. And wants more. Ever lasting pain for immortal humans. Until the end of time. Or until someday God may look down upon us, decided we have been in hell long enough, and grant us peace.