Is the snake his pet or something?

I know this might sound stupid but is the snake a seperate being or is it just part of Kabuto himself? We see him seemingly communicating with his snake on turtle Island, the snake was his tail when he escapes turtle Island, then the snake is conjoined during sage mode..

He summons a bunch of other snakes too, but why is this one always with him? It could be simply his design but are there any canon reasons?