The Japanese have a name for the finger-knitting exercise of the Ninja. It is called Kuji-Kiri, or literally, the "nine cuts." In the Hindu and Tibetan traditions, they are called mudras.Some schools add chants or mantras; others vigorously rub beads between their hands. Regardless, the hands are regarded as a microcosm of the body, so to stimulate or sedate the flow of energy and blood therein is certain to have an effect, even a mild or moderate one, upon the rest of the system.

Though the techniques of Kuji In and Kuji Kiri are closely tied to one another, they in all actuality serve two very distinct functions. The Kuji In hand positions are used to invoke nine levels of mystic power. They are a method of focusing the mind and activating these powers, each in turn. The Kuji Kiri, however, is a form of practical sorcery.

By associating specific meanings and symbols to each of these interlocking patterns, the Ninja were able to program themselves to withstand any torture or accomplish any feat. This gave rise to the legends of their superhuman prowess. And while the finger patterns had an effect on the user, because the knowledge of the connections of the hands to the body are known to everyone, albeit on a subconscious level in most cases, the patterns also had an effect on the audience. Thus, Kuji-Kiri is the Ninja art of influencing the minds of others as well as one’s own with unconscious gestures. When properly performed, the subject is totally unaware of being manipulated. 

Kuji-in is the spiritual and mental strength the ninja possessed in the form of hand signs. These hand signs were believed to be able to channel energy. The hand signs were taken from the practices of the early Buddhists. The Kuji-in was used to build confidence and strength in the ninja. It was also believed to enhance the senses of danger and foresee death for the user. In Kuji-in the thumb represents the source of power (Ku), and the fingers represent the four elemental manifestations. They are Chi (earth - solids), Sui (water - liquids), Ka (fire - combustion) and Fu (wind - gases).

There are 81 hand symbols in total total, but there are 9 primary ones: Rin, Kyo, Toh, Sha, Kai, Jin, Retsu, Zai, and Zen. Each symbol invokes different strengths and abilities in a trained ninja.

Rin brings strength to the mind and body; Kyo generates psychic power in order to mask one's presence; Toh enables the ninja to reach a balance between the solid and liquid states of the body,
which leads to a greater harmony with the universe; Sha is used to heal oneself or another; Kai gives complete control over the body's functions, enabling one to slow the heart rate, endure extreme heat and cold, etc. Jin increases the mind's telepathic powers, giving a highly trained Ninja the ability to read the character of another; Retsu gives telekinetic powers, enabling a ninja to stun an opponent with a shout or touch. Zai extends the harmony gained by merging with the universe. Zen brings enlightenment and understanding.