Ball 'O Hurt

The Ball 'O Hurt is an item under the Flails weapons category obtained by smashing a Shadow Orb with a hammer or dropped by Eater of Worlds. Similar physics to the Grappling Hook. It also puts off small particles similar to the ones put off by objects in the corruption. It extends to a certain length and then drops like it is affected by gravity. Automatically retracts if it hits a block or runs out of length.

It is particularly useful when fighting Bone Serpent or the Eater of Worlds boss, since it does relatively constant damage once you fire it.

Here is a guide on the Ball 'O Hurt