Snake Weapon

The Kuja all have snakes which can be used as weapons or other things. When not in use, the snakes wrap themselves around the body of the Kuja who own them. The serpents' bodies are about as long as the Kuja who use them, the exception being Hancock's whose body is exceptionally long compared to the others. Also they all wear small berets and a scarf, with the exception of Hancock's snake who wears a skull on it's head and appears to have some form of furry scarf around its neck inside of a normal cloth one.

When the snakes form into their various shapes, no word is spoken by the Kuja (a seen of yet) to instruct the snake to form the shape it does. How the snakes know which form to take is uncertain.

Weapon use
Bow: first snake weapon used by the Kuja. The snakes form a bow shape position with strings behind them. They are capable of firing projectiles such as arrows like normal bows. In recent chapters it has been revealed that the arrows fired by the snakes are embodied with Haki.

Other Uses
Staff: Elder Nyon's snake is seen in the formation of a staff, however it has not been seen for battle use. in Chapter 521 however it has also been used as a stepladder for the Yoda sized elder to speak with Boa hancock, her sisters and Luffy.

Chair: Boa Hancock was seen using her oversized snake as a chair in her bed.

Ropes: Small snakes are used to tie up Luffy. Luffy states the snakes are as strong as steel.