"Snake can talk and bite."

Interesting detail. If the sword is known to bite, it's an effective guard against thieves, since it's part of the sword, and cutting at (trying to destroy the snake guardian) the snake possibly ruins the sword or it's magic too, rendering it to an ordinary sword, not much worth. That means the snake guard is a must-have part of it's design. Effective guardian indeed. I imagine it recognizes it's owner so it can be safely carried around, but maybe to draw it, one must also say an activation word to awaken the guardian and let it's grip loosened on the handle and sheath. If so, a silence spell could be it's weakness. If the guardian is hyper intelligent, it may be ever-alert and allow usage to any persons who are known friends/good family/allies with the owner to protect them or get the sword back to them...or in the case of death choosing the next owner.

About talking. How much intelligence it has? It may be low, and just able to greet the owner, tell about things it heard, or about persons who tried to steal it, maybe warn against sneak attacks, or have high intelligence and outright act as a companion to it's owner, and have conversations with them, maybe even tell tales about previous owners and legends it heard.