The Needle at Sea Bottom ( 海底针, Hǎidǐ zhēn) is a posture found in t'ai chi ch'uan. This set is a move involving a half step back, rotation to the rear, and pushing hands from a high position down in front of the forward leg. Involves Tsai, developed out of a movement similar to the Brush Knee and Step Forward movement.
The Needle at Sea Bottom is an relatively dificult posture to learn to beginners, since it requires mastering a really low Xu Bu stance, while mantaining coordination, balance and strenght.
This posture features the Tsai (Pulling Down) application and a Chung Ting (Central Stance) movement.