A rag and bucket are like so five years ago. If you really want to get the truth out of someone, head to the Machine Project's Lie Detector Workshop and build your own truth-telling machine. Using electronics, the group will make their own "lie detector" in the form of a galvanic skin response meter. The machine measures the electrical conductance of the skin, which varies with moisture and as you sweat. Not sure it's intimidating enough to draw out super secrets, but it can at least hold you over until you have time to make that dog collar.