Suspicious Looking Eye

The Suspicious Looking Eye is a consumable item that summons the Eye of Cthulhu. It is likely the first summoning item the player will obtain, and requires a Demon Altar or a Crimson Altar to craft with 6 Lens. In addition to being crafted, they can also be found in Gold/Frozen Chests in the Cavern and the Dungeon, or in Ivy Chests in the underground Jungle.

The Suspicious Looking Eye will only work at night. If the player tries to use it during the daytime or when another Eye of Cthulhu has already been summoned, the Eye of Cthulhu will not spawn and the item will not be consumed.

Trivia

 * The Suspicious Looking Eye is the upside-down icon of a Servant of Cthulhu.
 * It is one of the few suspicious-looking boss-summoning items in Terraria, the others being the Suspicious Looking Skull and the Suspicious Looking Egg.