That one was, because it was possessed by Satan, and he can talk.
In Genesis, 3:12-13, the man says,
quote:
'The woman whom thou gavest to be with me, she gave me of the tree, and I did eat.'
and the woman says,
quote:
'The serpent beguiled me, and I did eat.'
If the serpent was possessed by Satan, and was therefore able to talk, why didn't God ask it why it had beguiled the woman? I'm sure a lot of people would be very interested to know, and even the serpent had a right to say something in its defence.
Also, if the serpent was possessed by Satan, one could argue that it was not responsible for its actions. If so, why did God punish all natural snakes by forcing them to march on their stomachs, like Napoleon's army?