Satisfied that the scorpion won't sting him – because then he would drown too – the frog agrees. Half way across, the scorpion stings him anyway.
"Why?" gasps the dying frog.
"Because it's in my nature to sting," responds the scorpion.
For a few weeks the scorpions have sheathed their stings at Westminster and all those remote locations where they are finding themselves and video conferencing in.
You can sense that from the start this consensus and "working together" stuff has been increasingly maddening for them. It is just not in their nature.
And the current state of politics is a reminder that politicians can only hold themselves back for so long before they start to sting again.
All that unity guff which comes so unnaturally to them is now departing out of the window. Normal disservice is rapidly being resumed.
Frustrated that coronavirus, an indiscriminate global pandemic which has hit rich and poor countries, capitalist and communist, has been insufficiently political, they are now finding ways to politicise it. That means that it has to be somebody's fault.
With there being 40,000 deaths, and counting, Boris Johnson is in a vulnerable position. It isn't what he had in mind for Britain when he came to power after his general election victory. Whatever he does, there is no spinning away 40,000 deaths.
It hasn't even started yet because we are heading for a recession and massive job losses. On top of that there is the massive borrowing that's been required for measures like the furlough scheme. It's going to take years to pay for.
This is Boris' banking crisis. Back in 2008 the global banking crisis wasn't the fault of Gordon Brown and Alistair Darling. Nevertheless when it landed with a thud on their desks they were left with a choice of letting banks go bust and huge numbers of ordinary people losing all their money, or not letting the banks go bust but at tremendous cost to the nation.
The economy was sent into a nosedive and the Tories put the boot in. It is now written in stone that Labour crashed the economy.
But now the boot is on the other foot. With the economy going off a cliff edge, it would be an act of huge political forbearance for Labour to go easy on the Tories.
Protestations that "it's all because of the coronavirus crisis" will be treated in the same way as Labour's protestations that it was "all because of the banking crisis" during those far-off days when they were last in government.
New Labour leader Sir Keir Starmer's policy has been to look prime ministerial, responsible and supportive in the national interest, while subtly seeking to make the government look like a bunch of incompetent jackasses.
He's increasingly not bothering with the subtlety.
This week he waved the confidential letter he said he had sent to Boris offering to work constructively together on the reopening of schools, and complained he had not had the courtesy of a reply.
I should say that he waved the letter forensically and brilliantly, because as Sir Keir is a lawyer, everything he says and does is by definition forensic and brilliant.
Miffed by BJ's non response, he said he would put this confidential letter in the public domain.
So it's not confidential now. Personally, I do have a problem with that, even though the letter has created no ripples whatsoever so must be deadly dull.
Going back to the banking crisis aftermath, Labour's Chief Secretary to the Treasury Liam Byrne famously left a note for his successor in a drawer which said: "Dear Chief Secretary, I'm afraid there's no money."
Although on reflection he didn't know what on earth he was thinking of, at the time he saw it as a friendly word honouring an old tradition that stretched back to Churchill in the 1930s.
Instead of seeing this private note in the jokey light in which it was clearly intended, David Laws, his Lib Dem successor in the coalition government, and George Osborne, made full political capital out of it. And it was a gift for David Cameron to flourish during the 2015 general election campaign.
Liam Byrne, who had been a high flyer, was politically finished (he's still an MP, but it's unthinkable that he could ever again achieve high office) and beat himself up for his own stupidity.
It was a mistake for which he blamed nobody but himself. But his real mistake had been to trust politicians to be able to take a private joke.
Or, to put it another way, he underestimated the willingness of the Honourable and Right Honourable Members to go low if it was to their political advantage.
Now it's payback time for Labour.
Sir Keir Starmer has open goals opening up.
When it comes to coronavirus, the gloves are coming off.