Bloody Tear

The Bloody Tear is an item used to summon the Blood Moon. It can only be used at night; attempting to use it during the day will not commence the Blood Moon and will not consume the item. It is dropped with a chance from the Wandering Eye Fish, Zombie Merman, Blood Zombie, Drippler, Clown, Blood Eel Head, and Hemogoblin Shark, and with a  chance from  The Groom, The Bride, and Dreadnautilus.

Trivia
The tooltip is a reference to Castlevania II: Simon's Quest, in which the game would show up the same text whenever it became night.