The Lucky Mojo website states that wishes are made with wishbones by two people each grasping a leg of the bone and then pulling it apart at the middle until it snaps, while making their wishes. The person with the longest piece of the bone after it snaps is supposed to have his wish come true. On those occasions when the broken lengths are even, both wishes are fulfilled.
The belief in a wishbone being able to grant a wish was once commonplace both in the United States and in the British Isles, where the bone was known as the merrythought. The bone itself is considered to have no mystical power until it's broken during the ritual. In order to prepare the bone for breaking, it is carved whole from a chicken or turkey during a meal and then dried. The drying can be over a stove or near a fire, or the bone can be air-dried for three days. The wishbone is ready to be broken when the moisture is removed and the bone is slightly brittle. Generally, the bone is given to children to break, and the wishes are kept secret, lest they not come true. The wishbone ritual lost its popularity during the 1990s.