Hanji's wife Yoshi practices "ohaguro" (literally: "black teeth"). In many areas of Asia, blackened teeth were considered a sign of beauty and maturity. In Japan, the practice was banned by the government in 1870.
The "mon" coins used by the gamblers were made of either copper or iron and were the lowest-denomination currency in Japan until the yen system was established in 1870. The "ryo" paid to Zatoichi were gold and were worth many thousands of "mon." The Currency Museum of the Bank of Japan estimates that one "ryo" would be worth roughly $1200 to $1300 now.
Just before Shigezo leaves for battle, his wife strikes a flint over his shoulder. This was a common good luck custom that evolved from an ancient Shinto spiritual ritual.
In his drinking scene, Hirate performs several series of moves with his katana (Japanese two-handed sword) from a kneeling position. This is Iaijutsu, the art of the quick-draw and its requisite zen-like presence of mind. Iaijutsu comprises many forms for drawing a katana to attack or to parry and counter-attack from any position at any moment. The katana is always returned to its scabbard to end each form. The word Iaijutsu means, literally, "the practice of constant readiness."
The weapon that Zatoichi used called the cane sword is usually made from a low-quality steel and often considered inferior when matched even to a low-end katana.