David Cameron's attempts to wind Gordon Brown up appeared to be succeeding. But a burst of unexpected comedy from the prime minister helped restore his benevolent mood.
After the pomp and ceremony of the Queen's Speech this morning, it was time for a return to normality this afternoon. Namely, Cameron bashing Brown to bits.
His initial efforts failed; Brown merely simpered inanely when he was told "the NHS is not this government's first priority". He flashed a Blairite grin at the opposition benches when Cameron called him "incompetent".
And when the Tory chief demanded he stand up and explain himself on one point or another, Brown very deliberately engrossed himself in conversation with his next-door neighbours.
"We've just seen from the prime minister - they've run out of courage as well," Cameron said theatrically. Brown, legs crossed, rocked himself to and fro, smiling placidly.
He even had to stop himself bursting out laughing when Cameron attacked his 'government of all the talents', or 'goats' for short.
"We've had so much ermine wasted," Cameron said. "Never have so many stoats died in vain." This was deemed hilarious by the entire House, which roared with laughter. "Stoats for goats!" Cameron blared. politics.co.uk can confidently guess that was the first time that phrase has ever been used in this parliament's history.
As Cameron warmed up and got these bizarre expressions out of his system the momentum began to shift. Brown's smile slowly shifted to a scowl as the leader of the opposition demanded "political leadership" from him.
Then came a key accusation: "You've got an opposition behaving like a government, and a government behaving like an opposition." There is more truth in this claim than Brown would care to admit. The blows kept coming, to the delight of backbenchers behind Cameron.
"They've been a monumental failure for the country... he's desperately trying a few tricks to save his own skin... why doesn't he just get on with it [and call an election]?"
Brown, who as usual defused the tense situation by paying his condolences to fallen Afghanistan soldiers, was by now in danger of slipping into his usual filthy mood. He found it difficult to get himself going in response, but managed to distract himself with some very light humour at the expenses of his slavishly loyal backbencher Emily Thornberry.
Thornberry, the seconder of the Common's motion for a loyal address to Her Majesty, had had her trip on a husky-driven sledge in the Arctic Circle initially raised by Cameron. Brown decided to raise it again to get in a little dig at the leader of the opposition.
"History does not show if these were the same huskies who that same year had an encounter with the leader of the opposition" - he paused, turning around to deliver the punchline - "and a passing cameraman".
Labour MPs laughed hesitantly; Tory MPs found its clunkiness hilarious. Brown stepped backwards, his mouth lolling downwards as his body shook with hearty glee. He had made a joke! He was the prime minister, and he had made a joke!
It was almost too much to bear. How could any politician return to the cut-and-thrust of political debate after this comedic breakthrough?
He got a much bigger laugh when he went on the offensive against the Tories. Telling them that they were a party "rent asunder" by Europe was, perhaps, a little wordy. Conservative MPs shouted it back at him as if they had learned a dirty new phrase. "Rent asunder?!" they giggled. "Rent asunder!!"
A much more effective attack came in response to a question about inheritance tax, which, Brown claimed, would only benefit those in the Kensington and Chelsea borough. In fact this was probably the best line of the entire day, "rent asunder" notwithstanding. It restored the prime minister's good mood entirely.
"This must be the only time a tax change in history when the leader of the opposition, the shadow foreign secretary and the shadow chancellor will know by name all those who will benefit," he observed. The Commons erupted. "Is this what they mean by 'we're all in this together'?"
Now that really was funny. Brown's cheerfulness was fully restored, leaving Cameron scratching his head. Perhaps he was wondering why his barbs hadn't met with their usual success: maybe Brown was trying smile therapy?