From Zelda Wiki, the Zelda encyclopedia
An Arrow Orb as seen in-game
|Game(s)|| Phantom Hourglass|
|Use(s)||Redirects a shot arrow|
Found in dungeons, an arrow orb's function is to redirect an arrow towards a determined direction when Link hits it with said arrow. The direction of the shot depends on the position of the golden curvy pointer that surrounds the orb. When hit with the sword, boomerang or whip, the orb moves the pointer clockwise to a new direction. Sometimes this can be done to hit switches that unveil secret Treasure Chests.
When an Arrow Orb is doing its function, the game shows the shot arrow's motion through a cutscene; this is done so that one can see what the arrow will hit in the end. It's possible to guide a shot arrow with multiple Arrow Orbs and, in Spirit Tracks, they can be carried by either Link or Princess Zelda to customize a new shot trajectory. This is important to solve otherwise impossible puzzles.
There is a glitch involving two orbs constantly interchanging the arrow shot by Link.