Horse Call
The Horse Call is a horseshoe-shaped flute acquired by Link in The Legend of Zelda: Twilight Princess. It is used to play Epona's Song to summon Epona anywhere in Hyrule Field, similar to the Epona's Song from The Legend of Zelda: Ocarina of Time. It eliminates the need for Link to locate patches of horseshoe grass.
WARNING: Spoiler Alert!
The flute was made by Ilia as a gift to Link for his journey from Ordon Village to Hyrule Castle. Before Link could depart, however, a group of Bulbin raiders appeared and captured Ilia and several of the other Ordon children. Eventually, Ilia found her under the care of Telma in Castle Town, though suffering from memory loss. In a quest to restore her memory, Link recovered the flute from Impaz in the Hidden Village, where Ilia had been held captive. After presenting the flute to Ilia, she regained her lost memories and was finally able to give Link his gift.