Somewhere near the center of Palermo, in Sicily, there is an old amusement park.
Should you wander around, just aside a shooting gallery there is an old funny-looking statue of a grotesque face. Don't try to get close to it yet. As soon as you're about to touch it, no matter how hard you try, you'll change your mind.
Go to the shooting gallery and pay the clerk for three games. It will cost you the equivalent of $10 in total. It doesn't matter how much you score. As soon as you finish the second game keep the gun and don't shoot again. The clerk will ask you for his gun back, but you must ask to try the Mouth of Truth instead.
After he agrees, you'll be able to approach the statue. Put your hand in its mouth up to your wrist. A small crowd will gather around you. After some seconds the eyes will light and your hand will be blocked, as the statue will ask you one question about a secret, or embarrassing fact of your life, even something you're ashamed of. You must answer the question truthfully and aloud, regardless of the people watching you.
If you answer correctly, some will be shocked, others amused by the truth, and your hand will be released. Within the following two or three weeks you will feel somewhat different.
You will see that same light of the statue in your own eyes, and you'll notice people will feel a bit uneasy when talking to you. That will be for a simple reason: none will be able to lie to you. The effect of this "blessing" will last about a year. After it has worn out, you'll be able to redo this once again.
Don't answer the statue with a lie! An inner mechanism will clamp your fingers and you'll pass out from the shock. When you wake up, you'll be just outside of the park, and you won't be able to enter it ever again. When you'll go back home, the morning afterwards you'll feel something strange in the hand you put in the statue's mouth, and find out your pinky is missing. There will be no cuts or wounds, just smooth flesh where your finger used to be.
Throughout the following days, each morning you'll wake up with one of your fingers gone. On the eleventh to twentieth morning your toes will start missing. Should you try to ask for help, people will just laugh at you and tell you've always been a liar.
By a month, you'll have no appendages: no nose, ears, eyes, lips, genitals. All you'll be able to is feel around with your stumpy limbs. Then your limbs will disappear too. You'll be left wherever you fell asleep as a human stump until starvation and decay get the better of you.
If you answer truly, but keep your voice low, from that moment on for the rest of your life you'll just be a big liar. Any time you try to tell the truth, your voice will be cut and only a slight hissing sound will come out.