Perhaps it was the invigorating effect of winning 823 new councillors. Perhaps it was the fact that this Queen's Speech was obviously not a game-changer. Perhaps it was the prospect of a whole new raft of bills to clog up the coalition, including the Lords reform nightmare. Whatever it was, Ed Miliband was in a very chirpy mood this afternoon.
Following the morning's political theatre, where we (the royal 'we', there) watched the Queen open the new parliamentary session with her usual restrained dignity, this afternoon it was time for the real politics to begin. Well - almost. The motion to thank the Queen for her gracious address first had to be proposed and seconded by two government backbenchers. Tradition dictates that they begin the parliamentary session in the way it will go on and on: with long-winded, largely irrelevant, occasionally irreverent speeches.
Nadhim Zahawi, the MP for Stratford-on-Avon, had his moments. He reminded MPs that he had once worn a novelty musical tie in the Commons chamber and quoted Shakespeare's wise words on the dangers of too much haste when using Twitter. He was followed by Malcolm Bruce, the Liberal Democrat veteran of Gordon, who suggested the best reason to vote 'no' in the Scottish independence referendum was that independence would result in Alex Salmond being seen in public wearing a kilt. The economy is in double-dip recession and the spending cuts are starting to bite, but parliamentary niceties - of which this charade was one - must be observed.
It was after this 40-minute warm-up had finally wrapped up that we came to our main feature presentation: the leader of the opposition's opportunity to lay into the government's proposals with aplomb. Miliband did not hold back, but first reserved some praise for Bruce and Zahawi. The latter had set up the pollster firm YouGov, which Miliband admitted with a smile had "a lot to answer for". "No doubt," he added, "the prime minister feels the same." The inference was clear: Ed had been under fire because of the polls, but now it was Dave's turn to feel the pressure. Cameron smiled wryly. Ed Miliband flashed his teeth.
He has an unusually gleeful grin, the kind of gloating silent chuckle that must make him an insufferable Monopoly winner. Miliband was obviously enjoying last week's elections success. He grinned as he pointed out one Liberal Democrat candidate had got less votes than a penguin. He grinned as he quoted Boris Johnson saying he had won the London race despite the endorsement of the prime minister. He grinned when he quoted Nadine Dorries calling Cameron and Osborne "arrogant posh boys". This exultant approach is effective, in that it winds the Conservatives up no end. If Ed Miliband ever does win a general election, he will be unbearably smug for months.
Cameron and co were, by contrast, very sullen and withdrawn. The prime minister appeared to be trying to ignore Miliband as the Labour leader got up a head of steam, attacking the coalition for the "recession made in Downing Street". Miliband isn't afraid of playing the man and not the legislative package. "He's gone from David Cameron to David Brent," he said scornfully. Cameron sat there, fuming to himself. It was only when Miliband criticised the lack of a full bill on reforming adult social care that he exploded. The prime minister started flapping his hands around wildly, trying to swat away an imaginary fly and flashing fingers at Miliband. Not like that - he was indicating '13 years' to point out Labour hadn't done anything about it. Still, this was unusually theatrical behaviour from Cameron.
"Thank you, Mr Speaker," he said, nodding firmly to John Bercow, drawing strength. He tried to calm the atmosphere down, jokingly recalling mishearing that it would be 'Nadeen' rather than 'Nadhim' opening the debate. But the opposition remained as dismissive as ever. Lines like "It is a Queen's Speech for the doers, the strivers, those who play by the rules" read well when written down, but sound a little trite when uttered aloud.
Strangely, I spotted something I don't think I've ever seen before: as Cameron pressed on with his response to Miliband I noticed that his hands seemed to be shaking. I've been watching David Cameron deliver speeches and statements in the Commons, Downing Street and elsewhere for years, and have never seen him in this state before. But there it was, definitely the case: a tremor in his right hand whenever he raised it above the despatch box. The PM is an assured parliamentary performer and has got used to the big occasions by now. Still, it was definitely there. Cameron's adrenaline, it seemed, was well up and running.
Fight or flight: the PM has no option but the former, and so stuck it out bravely. What a contrast with the man opposite, a politician whose star had almost faded irretrievably before he was rescued by the government's omnishambles. While David Cameron's confidence looks like having taken a major blow in recent weeks, Ed Miliband is very much in the ascendant. As his delighted, comic-book grin revealed at regular intervals this afternoon.