It's a mistake anyone could make. Your pet cat is looking a bit peaky, so you pop a couple of aspirin into its food. Bad idea: aspirin may be a virtual panacea for humans, but it causes respiratory problems and hepatitis in moggies. Still, it could have been worse: give a cat paracetamol and you'll kill it.
The lesson is clear - and well-known to every vet. Much as we might kid ourselves, our pets really aren't human. Drugs do things to them that they don't do to us. And vice versa. Therein lies the real argument against animal testing and it has nothing to do with "animal rights".
Yesterday saw a ruling by the Advertising Standards Authority. It centres on an allegation made by the anti-vivisection pressure group Europeans for Medical Progress. In one of its leaflets the Liberal Democrat MP Mike Hancock is quoted as saying that "animal testing has never been scientifically evaluated".
Not surprisingly, this incensed scientists and a group of them formally complained to the ASA. Now the ASA has rejected the complaint, but seems to have struggled with the fact that Hancock is right: animal testing has never been subjected to scientific scrutiny. When a new drug has to be tested, no-one knows for sure if the outcome has any relevance for humans.
Just ask those six young men who ended up fighting for their lives in a London hospital last year after volunteering to test a "wonder drug" called TGN 1412. They had drawn comfort from the fact that - as with all drugs today - TGN 1412 had already been tested on animals who had shown no ill-effects.
Better still, the volunteers were to receive a far lower dose than had been given to the rodents, dogs and monkeys used by researchers. Yet, within minutes of being injected, the volunteers suffered terrifying effects on their immune system.
There's no doubt work involving animals has brought huge medical advances. Over a century ago, the then-controversial claim that disease can be triggered by tiny microbes was first confirmed by injecting animals with bacteria. Surgery has also benefited from techniques first tried on animals with organs bearing obvious similarity to those of humans.
But this is a world away from testing drugs, where subtle differences in biochemistry can lead to dramatically different results. For instance, of around 100 therapies for stroke that have produced promising results in animals, just one has proved effective in humans: a 99 per cent failure rate.
Animal tests don't just fail by letting harmful drugs slip through the net, sometimes compounds that might work perfectly well in humans kill lab animals - as with cats and paracetamol. Antibiotics like penicillin, anti-nausea treatments and even aspirin all produce serious side-effects in some lab animals. Fortunately, many of these were found long before the introduction of mandatory animal testing, or else they might never have been approved. But just how many other wonder-drugs are we missing because scientists were misled by side-effects in animals?
Supporters of animal testing like to paint their critics as irrationally anti-scientific. And, over the years, animal rights activists have done themselves no favours with their bullying, often violent protests.
Supporters of vivisection also like to claim that virtually all of today's wonder-drugs have benefited from animal research. Yet, as animal testing is mandatory, it's no surprise that every breakthrough has been through this testing. It's as rational as crediting scientific breakthroughs to the wearing of lab-coats.
Then there's the TINA argument - that There Is No Alternative to using animals. Yet research into replacements, ranging from computer simulations to individual human cells, is well-advanced. Better still, their reliability is being checked scientifically - something that has never happened with animal testing.
Of all the arguments used by supporters of vivisection, the most damaging is that you're either with the scientists or with the animal rights terrorists. It has been turned into a no-win debate and hides the fact that many critics are prepared to accept that animals can sometimes prove useful in research. All they ask is that testing be put on a rigorous scientific basis. Until then, the issue of animal testing will be monopolised by the emotional and misinformed. The fact is, scientists often end up using animal testing as little more than a fig-leaf to conceal their ignorance from their patients.
Robert Matthews is Visiting Reader in Science at Aston University, Birmingham
Reproduced by kind permission of Robert Matthews & the Daily Express