Oh it was beautiful. He was teasing the demon. Giving him 'a chance to escape'. There was nothing in all of Hell or Earth more entertaining than false hope. It had been the favourite trick of many of Alastairs torturers, herself included during her initial change into what she was. Dean might have been the protege but Sam wasn't doing too badly.
It helped that she was better than Alastair. Maybe not as skilled but she was better, in ways the other demon never would have understood.
First one leg was taken, then the other leaving the demon to crawl, Ruby held the door in place with her power just in case, but she didn't think Sam would let him get there, or if he did he'd have noticed the quick, sharp movement of her hand, the demon didn't, he was too busy with his desperate attempt to surrvive.
Twenty Seconds.
Fifteen.
She didn't even hide the smile anymore, she didn't need to, this was just some poor excuse for a demon that Sam was putting out of its misary, and he was relishing it just as much as she was.