IF you want to hear what a true bum note sounds like, an harmonically pure clanger, try eight minutes into FMQs, when Kezia Dugdale asked Nicola Sturgeon about education.

Tory Ruth Davidson had just pressed the First Minister about a new Sutton Trust report into the slow puncture mocking the reputation of Scotland’s school system.

As education is Ms Sturgeon’s “defining priority”, the Labour leader raised it too.

At which, the mass of SNP MSPs let out the sort of bored, dismissive groan you’d expect from the back of detention class. Really? Do we have to? Learning’s for nerds, Miss.

Ms Sturgeon looked mortified. Presiding Officer Ken Macintosh called for order.

“They can groan all they like, but it is true and they should read it,” snapped Ms Dugdale.

Brow furrowed like a well-thrashed tawse, the FM put her charges back in order.

“I say it is an important report,” she reminded them. “I absolutely accept that.”

And in case that didn’t penetrate their roomy skulls: “Every politician in the chamber who raises issues about education is absolutely right to do so.”

The echo of that groan seemed to throw the Nats off their stride for the rest of the session.

Even rubicund know-it-all Stewart Stevenson thought Ms Sturgeon had been promoted.

“Did the Prime Minister,” he addressed the FM, before attacking Labour MPs for “signing a blank cheque” to the actual Prime Minister to determine the terms of Brexit.

That, he raged, gripping his lectern like a Tory throat, meant a “sell-out” of Scottish fishing.

Ms Sturgeon said should nobody be surprised by that as the Tories had done it before.

Nor, to the cynical among us, was Mr Stevenson’s question much of a surprise, as the FM had come with a pre-cooked soundbite.

But with that off note unsettling her, she ended up flogging the gag to death.

Labour voting for Article 50 showed what a crummy opposition they were, she said.

“I saw Jeremy Corbyn tweeting last night that the real fight begins now. How utterly pathetic.

“It’s not so much bolting the stable door after the...” she stumbled.

“Closing the stable door after the horse has bolted,” she corrected herself.

She fell to marking the beats of her practised answer with bobs of her fist.

“It’s more like closing the stable door after the horse is dead,” she blurted. “And buried,” she remembered.

Finally, Tory newbie Oliver “Son of David” Mundell asked if she could guarantee his and dad’s constituents there would be no Indyref2.

“On the question of a second referendum, I have been very clear about my determination to find compromise,” said Ms Sturgeon without blushing. We all groaned at that one.