Something I-T came up with during an "essay competition" and the sad soul that I am, I retained it somehow, here goes.

Proof that all cats have 9 tails:-

As we know from general consensus, 1 cat has 1 tail and no cat has 8 tails.

Therefore, (no cat + 1 cat) has 9 tails.

Also, according to popular opinion, 1 cat is the same as all cats.

Therefore, all cats have 9 tails. :|