Cruciatus Curse

The Cruciatus Curse is an Unforgivable Curse that causes unbearable pain. Its incantation is Crucio. Alice and Frank Longbottom were tortured to the point of insanity with this curse.

The pain that it cause is supposed to be worse than 'one thousand red hot nails, boring into the skin.' This makes it popular among the Death Eaters, for use on both enemies and muggles. Lord Voldemort is particularly fond of this curse to keep his Death Eaters in line and loyal.

This curse is also a favourite of Bellatrix Lestrange, who was convicted of torturing the Longbottoms with it, and later used it on Neville Longbottom in the battle in the Department of Mysteries.

In order to perform this curse, you have to want to enjoy causing the victim pain, as Harry Potter found out when he tried to use it on Bellatrix Lestrange. This follows suit with all the unforgivable curses, as Barty Crouch Jr (then disguised as Mad Eye Moody) explained to the 4th year class in Harry Potter and the Goblet of Fire (film). Unforgivable Curses "need a powerful bit of magic behind it -- you could all get your wands out now and point them at me and say the words, and I doubt I'd get so much as a nosebleed." (GoF pg 217/192)