[The urumi is] a long sword made of flexible steel, sharp enough to cut into flesh, but flexible enough to be rolled into a tight coil. It was used and still can be found in Kerala, and is one of the weapons learned by practitioners of the martial art of Kalaripayattu. It was most popular in the North Malabar Coast of Kerala state, India, and is often mentioned in the ballads of the region.
The flexible sword is called Urumi in the Northern System of Kalaripayattu and Chuttuval in the Southern System. The word Chuttuval . . . is derived from the Tamil roots Chuttu . . . (coil/spin) and Vaal . . . (sword) and means Coiled Sword, a very apt description of the way the sword is maneuvered by the swordsman. Since the sword is flexible, and worn curled around the waist or bundled into the belt, it has to be straightened out, which is generated by turning it around the wielder's body mostly in a vertical plane. Urumi is still practiced in all kalaris.
An interesting side note: the word urumi comes from Malayalam, a Dravidic language with the distinction of being a palindrome.