"It's very heavy, very expensive, and very, very poisonous.  Oh, and people with little black plastic badge cases and no sense of humor tend to take an interest in you when you try to buy some on the open market."  Junior regards Antonio for a thoughtful moment, then adds, "Think about what would have happened to you if you'd tried stealing a book or three of black magic from the Vatican library.  It'd be kind of like that.  Only more so."