Am I going mad or is this unclear...?

[Ginshizz]

I have just been asked to review some advertising concepts for a client and one has left me very confused. I have changed some of the wording so my client's identity is not obvious but please can I have your thoughts on what this sentence means:

"A cat needs a mouse, not a computer"

Does this mean:

a) A cat does not need a computer; he or she needs a mouse.
b) A computer does not need a mouse; a cat does.

I think it means a). But the ad agency think it means b). I am slightly thrown because a professional copywriter wrote this so I think he should know about these things.

Argh!

All thoughts gratefully received

I agree that the wording "A cat needs a mouse. A computer does not." Is much clearer.

Also, a cat doesn't NEED a mouse, does it? It may WANT a mouse, but it could survive perfectly well on other types of food.

Cross posted there.