The Tarovian neck pinch was a move which Nardole learned from studying Tarovian martial arts. When he used it on Alan, the man was knocked out instantly.
While a skilled Brown Tabard, Nardole could only perform the act with his original right hand and not with his left hand, which was in fact a replacement he had won gambling. (TV: The Lie of the Land)
Behind the scenes Edit
The move taken by Nardole is very similar to that which Ian Chesterton used in TV: The Aztecs to defeat Ixta quickly in combat, using only his thumb.
The Tarovian neck pinch is likely also a reference to the Vulcan neck pinch from the Star Trek universe, especially since after performing the move, Nardole then remarks "Let's trek on."