http://www.telegraph.co.uk:80/news/main.jhtml?xml=/news/2007/11/09/ncats109.xml
The above link tells the story -

Hundreds of cat owners are accidentally killing their pets by using flea treatments meant for dogs.

A study, by the Veterinary Poisons Information Service (VPIS), warned cat owners against using flea preparations designed for dogs that contain a chemical called permethrin.

It found that 97 per cent of cats treated with the chemical showed signs of poisoning, 88 per cent suffered twitching and convulsions and 10.5 per cent died or were put down. Permethrin is highly poisonous to felines.

Poor cats, thank you for posting that, who knows it might just save someone mistakenly thinking its ok to use dog flea treatment because they have run out of the cat one.... if I'm honest I didn't know they were different I thought they were just obviously made for different weights, although I have never thought to use the dog one on my cats or visa versa.

Frontline spray can be used on both dogs and cats

Frontline spray can be used on both dogs and cats

But only the one that says cats and dogs, there is a dog only one and a cat only one too. :)