The Vulcan death grip was a fictitious Vulcan technique, apparently invented by Spock. Its application appeared similar to that of the mind meld, but it was administered with two hands, and without speaking. It was supposed to be deadly pressure applied to the face and head.
In 2268, Spock used the so-called "Vulcan death grip" on Captain James T. Kirk as a means to fool the Romulans into believing Kirk was dead, so as to bring him back on board the USS Enterprise without causing suspicion. Spock claimed that he had used the death grip instinctively, in response to an unexpected assault from Kirk. Dr. Leonard McCoy angrily spat, "Well, at least your instincts are still good, Mr. Spock. THE CAPTAIN IS DEAD!!!"
In reality, Spock had administered an especially deep nerve pinch to Kirk to falsify the latter's death and also to block Kirk's life-signs from Romulan bio-scanners. When he recovered, Kirk complained of his neck feeling like it had been twisted off--apparently, this was from the stabbing pain of an actually physically pinched nerve.
When informed of the incident, Nurse Christine Chapel exclaimed, "But there's no such thing as a Vulcan death grip!" Kirk replied, "Ah, but the Romulans don't know that!" (TOS: "The Enterprise Incident")