Stone of Agony
The Stone of Agony is a magical stone that will vibrate when an unseen secret is close to its holder. It has a unique shape, like that of its real-life counterpart, the Nintendo 64 Rumble Pak, and also possesses the symbol of the Triforce etched upon its surface. Link acquires the stone as a reward from one of the cursed residents of the House of Skulltula in Kakariko Village after destroying 20 Gold Skulltulas. Possessing the stone within the game will activate the Nintendo 64 Rumble Pak and cause the player's controller to vibrate when a secret it close.
The stone is a companion relic of two other items: the Mask of Truth and the Lens of Truth.[1] When all three items are used collectively, a traveler can often find his way much easier and have a firmer grasp of the true nature of their surroundings. The stone material itself was cut long ago from an enchanted Gossip Stone of Hyrule, which is where it acquires its sensitivity to nearby secrets and clues. It is speculated to be part of a set of three objects, including the Lens of Truth and the Mask of Truth, that were created to give their holder untold power in terms of perception of the truth of their surroundings.