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. In addition to being crafted, they can also be found in chests in the Cavern.

First of all, The Suspicious Looking Eye will only work at night. If you try to use it in the day, no eye will spawn and the item will not be consumed (it will not disappear). If used when an Eye of Cthulhu is already spawned, it will kill the player instantly. Despite this, it is possible to legitimately fight two Eyes at the same time: if the message "You feel an evil presence watching you..." appears, an Eye can be summoned, but this will not cancel out the Eye that was already set to appear, resulting in a second Eye joining the fight soon after the first one does.

Trivia

 * Resembles a Demon Eye or the Eye of Cthulhu itself.