Question: when does a grass-fed cow stop being a grass-fed cow?
Answer: whenever you like, provided you are making the rules.
Mark my words: this is a question that is going to vex a lot of farmers for years to come.
The Irish beef sector is on the verge of launching its most important rebranding project ever.
Over the coming weeks, farmers and consumers will see the fruits of years of research, lobbying and multi-million-euro promotional campaigns heralding the start of 'grass-fed beef'.
It's not exactly revolutionary to suddenly claim that Irish beef is the product of years of grazing.
But as the Don Draper character in the TV series Mad Men proved in one of his strokes of advertising genius, a tin of beans could be marketed as so much more than a cheap nourishing staple.
His pitch reinvented the humble combination of beans and toast as a timeless tradition that bonded families together.
So when a consumer looks at a steak branded 'grass-fed', they are thinking about cows up to their waists in meadows, with their big lashes batting away butterflies flapping gently around their happy heads.
With Brexit pointing both barrels at the farm sector here, that imagery could be the saving grace of an industry that will be placing all its bets on improved sales on the Continent, in the US and further away in the likes of China.
The research is already complete. Of the 13,000 consumers canvassed by Bord Bia, two thirds said they are prepared to pay more for grass-fed beef.
So what is 'grass-fed'?
Again Bord Bia's research points the way. Some 60pc of consumers believe that it means that the animals have probably been fed other feedstuffs, but they've been grass-fed as much as weather and welfare constraints permit.
A quarter of punters believe that the animals have been 100pc grass-fed throughout their lives.
The last 11pc are the most pragmatic group - they reckon that regardless of how glossy the grass-fed label is, it doesn't really mean that much.
It's these last two groups that the industry needs to think most carefully about.
Consumers have so many resources at their fingertips these days that fudging this would be a fundamental mistake.
That's why I'd be wary about assertions that Irish grass-fed animals have a 90pc grass-based diet.
Glanbia make this claim in their promotion of their grass-fed cheese brand in the US.
But this neatly ignores the fact that on a drymatter basis that figure slips back to closer to 80pc.
I think that's still a pretty impressive figure.
The last thing the sector needs is consumer advocates picking holes in the numbers and asking why the calculations aren't done on a drymatter basis where everything can be compared like-for-like.
And when 20pc of the diet is non-grass, we also need to be looking at how that other portion is provided.
Consumers are becoming increasingly aware that tropical forests are being cleared to make way for ever more acres of soya and palm crops that in turn are being shipped around the world to be lorried into animals.
This is a point that Irish farmers have been shouting about for years but they also need to be sure that they aren't caught inside the glasshouse when they start throwing stones.
Feed imports into Ireland have doubled in the last decade.
Despite the fact that 100pc Irish-grown rations can be produced for little more than €10/t above the imported equivalent, there is still a general apathy within the sector about maximising the amount of native grain that makes up the remainder of the cow's diet.
Some of this is for good reason. The protein profile in soya is hard to beat for animal nutrition.
Equally palm kernel is very handy for dairy farmers to use as a buffer feed because cows don't gorge themselves on it the same way as something more local like rolled barley.
But where there is a will, there is a way.
Now that the Greens are back in power, they might look at a little carbon tax on those imported tonnes to try to focus minds?