I have always liked the threat of "If you don't cooperate, I can always talk to your corpse."
Personally, I may do the old "Hostile spirits speak in riddles." It gives a better chance of getting information if properly done.
I like both these ideas a lot.
PC 1: "Dead men don't talk."
PC 2: "Wtf are you going on about, they talk in entertaining riddles. Hurry up and slit this guy's throat so we can get at the fun brainteasers already."