Question: What torture technique did the successor of the Cheka agency use?
Context: Tsurushi (Japanese: 釣殺し ), or "reverse hanging", was a Japanese torture technique used in the 17th century to coerce Christians ("Kirishitan") to recant their faith.  Both Japanese and Western Christians are known to have been submitted to the torture.  As the tortured was held by the feet with a rope, one of the hands would be held tight with a rope, but another would be left hanging freely, so that a sign could be made by the tortured that he was willing to recant. Tean zu () is one technique of torture that was used in ancient China.  For interrogation of female suspects without threatening life or limb, zánzhǐ was generally applied.  It consisted of a set of six wooden sticks positioned around and between the fingers and connected by strings.  Each time the prisoner refused to testify or confess, the string was pulled, slowly, agonisingly squeezing the fingers between the sticks until their bones were crushed.  The Soviet KGB used a variant of this for crushing fingers or toes.  The kia quen, a similar device applied exclusively to men, was used to crush the feet or ankles. Psychological torture is a type of torture that relies primarily on psychological effects, and only secondarily on any physical harm inflicted.  Although not all psychological torture involves the use of physical violence, there is a continuum between psychological torture and physical torture.  The two are often used in conjunction with one another, and often overlap in practice, with the fear and pain induced by physical torture often resulting in long-term psychological effects, and many forms of psychological torture involving some form of pain or coercion. The KGB, an initialism for Komitet Gosudarstvennoy Bezopasnosti (Russian: "Комите́т Госуда́рственной Безопа́сности" ("КГБ") ; ] ), translated in English as Committee for State Security, was the main security agency for the Soviet Union from 1954 until its break-up in 1991, as a direct successor of such preceding agencies as Cheka, NKGB, NKVD and MGB, a committee was attached to the Council of Ministers.  It was the chief government agency of "union-republican jurisdiction", acting as internal security, intelligence and secret police.  Similar agencies were constituted in each of the republics of the Soviet Union aside from Russia, and consisted of many ministries, state committees and state commissions. Ivan Ksenofontovich Ksenofontov (August 29, 1884 – March 23, 1926) was a Bolshevik revolutionary and one of the founding fathers and leaders of the Soviet secret police and state security agency (Cheka, GPU and OGPU).  He gained notoriety as Chairman of the Supreme Revolutionary Tribunal and later as First Deputy Chairman of the Cheka, the agency's "number two" under Felix Dzerzhinsky, where he played a decisive role in crushing various anti-Bolshevik factions and the Kronstadt uprising; an early supporter of Joseph Stalin, he was described as Stalin's "mole" in the security services. Elements of the French Armed Forces as well as of the opposing Algerian National Liberation Front (FLN) made use of torture during the Algerian War of Independence (1954–62), creating an ongoing public controversy.  Pierre Vidal-Naquet confessed that there were "hundreds of thousands of instances of torture" by the French military in Algeria.  The Algerian National Liberation Front (FLN) were engaged in the use of torture against pro-French and uncommitted members of the Algerian population, to justify the use of torture (by the French). Zhou Xing (; died 691?)  was a secret police official of the Tang Dynasty and Wu Zetian's Zhou Dynasty of Chinese history.  He was largely responsible for carrying out her actions to wipe out senior members of Tang's Li imperial clan, but, in a turnabout, was in 691 himself accused of crimes and, under threats of a torture technique himself developed, confessed.  Wu Zetian spared his life and exiled him, but he was killed by his enemies on the way to exile. Medical torture describes the involvement of, or sometimes instigation by, medical personnel in acts of torture, either to judge what victims can endure, to apply treatments which will enhance torture, or as torturers in their own right.  Medical torture overlaps with medical interrogation if it involves the use of professional medical expertise to facilitate interrogation or corporal punishment, in the conduct of torturous human experimentation or in providing professional medical sanction and approval for the torture of prisoners.  Medical torture also covers torturous scientific (or pseudo-scientific) experimentation upon unwilling human subjects. Foot roasting is a method of torture used since ancient times.  The Romans immobilized the prisoner and pressed red-hot iron plates to the soles of their feet.  The Spanish Inquisition frequently employed an enhanced technique, binding the prisoner face-upward to the rack with the bare feet secured in stocks.  The soles of the feet were basted with lard or oil and slowly barbecued over a brazier of burning coals.  A screen could be interposed between the feet and the coals to modulate the exposure, while a bellows controlled the intensity of the flame.  Some of the Knights Templars are reputed literally to have been driven insane by the intensity and cruelty of the torture.  Variants included placing slivers of hot coals between the toes, or suspending the prisoner head-downward and placing hot coals directly on the soles.  Foot roasting remains a popular technique of torture to this day, though the modern variant typically makes use of a clothes iron applied to the soles, optionally complemented by the use of a soldering iron or electric wood-burning pencil to explore the delicate webbing between the toes. The Torture Technique is the second studio album by industrial rock band Sister Machine Gun.
Answer: Tean zu