Impossible he is clearly trying to something else than putting him in danger,he also said in a chapter that he wanted to kill Sebastian because he wanted to save Ciel's soul
Yes so true. I don't think he would try to bring Vincent back through Ciel. For one he is telling him to take care of his sole, tried to kill Sebby on the ship for Ciel's happiness, and at school he was worried for his life in general. He cares for him so deeply and want's to protect him.
True... I forgot about him saying those things..
I believe that Undertaker gave Ciel either an aphrodisiac, poison, or the mustard gas in a more liquid form.