Eye

Eyes are seen on a lot of occasions in Terraria.

Enemies:
 * Eye of Cthulhu, the first notable boss.
 * The Twins, the Hardmode counterpart.
 * Demon Eye, a common flying eye enemy.
 * Wandering Eye, the Hardmode counterpart.
 * Eyezor, a zombie with a large eye.

Items:
 * Suspicious Looking Eye, an item needed to summon the Eye of Cthulhu.
 * Mechanical Eye, an item needed to summon The Twins.
 * Eye of the Golem, an accessory dropped by the Golem.
 * Eye Spring, a pet summon item dropped by the Eyezor.