A method of psychological torture in which the victim was tied to a table with the head strapped down. Water was slowly dripped onto the victim's forehead until they cracked.
It doesn't sound that bad, but there are actual reports from people who experienced this who confirm that waiting for each drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip, drip was absolutely, terrifyingly maddening.