For the first time since Corbynmania began earlier this summer, the Labour backbencher and leftist rebel — now favored to become the Labour Party’s next leader when all the votes in the leadership contest are counted on Saturday — directly challenged prime minister David Cameron in the House of Commons on Monday.

Ostensibly, it was just another question about the Conservative position on admitting more refugees from Syria and abroad (see video above).

But there’s some fascinating body language that could show us what the future of British parliamentary politics will look like — and very soon.

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Corbyn, the MP from Islington North since 1983, has the distinction of bucking prior Labour leaders more than any other backbencher. But a surge of support for Corbyn, viewed by supporters as an earnest defender of British leftism, swelled the ranks of the Labour electorate. New members, presumably swept up by Corbyn’s charms, joined in the tens of thousands simply by paying a £3 membership fee. With the support of some of the country’s largest and most powerful unions, Corbyn quickly — and surprisingly — shot to the top of the pack against his three more moderate rivals.

Ironically, many of the 35 MPs who nominated Corbyn do not even support him; instead, they supported him to give Labour’s far left, previously an anemic force in party politics, a voice in the election.

There’s still a chance that shadow home secretary Yvette Cooper, who won plaudits last week for her strong stand on admitting more migrants to Great Britain, could win — and there’s a sense that she emerged only too late as the most ‘prime ministerial’ of the four candidates vying for the leadership. There’s still even a chance that the former frontrunner, shadow health minister Andy Burnham, could win. But oddsmakers are still betting on Corbyn to emerge victorious on Saturday. Voting opened on August 10, though many Labour voters have only recently received their ballots. Votes are tabulated on a preference basis — so if a voter’s first choice is eliminated after the first round of counting, the vote is transferred to the second choice and so on.

While Corbyn will almost certainly win the first round, there’s a chance that, as other candidates are eliminated, the anti-Corbyn vote will consolidate behind either Burnham or Cooper. The most moderate candidate, Liz Kendall, most associated with the policies of moderate former prime minister Tony Blair, is widely predicted to finish last.

Nowhere will that political earthquake create more tremors than at Westminster, where few members of the parliamentary Labour Party support Corbyn (pictured above), who may struggle to enforce the kind of party discipline he has so often bucked. Virtually no one believes that Corbyn will survive as Labour leader until the next scheduled general election in 2020 — and that it is only a matter of time before more seasoned Labourites hatch a restoration. Many senior shadow cabinet members flatly refuse to serve in a Corbyn-led opposition. Blairites (and Brownites) on Labour’s moderate wing worry that Corbyn’s 1980s-style socialism will doom the party’s chances in the 2020 election or beyond, and fear Labour could split, as it did briefly in the 1980s under former leader Michael Foot.

Corbyn is hostile to NATO, opposes Trident, Britain’s nuclear deterrent, wholeheartedly disagrees with the Cameron government’s push to balance the British budget through spending cuts, hopes to re-nationalize several industries (including British railways) and has called for a ‘people’s quantitative easing’ as a way to use monetary policy to improve the lives of the working class. Like Cooper, Corbyn is passionate about the need to take in more refugees. Unlike Labour’s leaders for the past 30 years, however, Corbyn is less enthusiastic about British membership in the European Union — and not committed to supporting it in Cameron’s long-promised 2017 referendum.

The sight of Corbyn, however, making what would otherwise be another backbencher’s plea — standing by himself in a speckled tie and a gray suit — spoke volumes about what life might be like when Corbyn is the new leader of the opposition. From day one, Corbyn will be isolated within Labour’s skeptical Westminster caucus, cutting an unlikely figure leading Her Majesty’s loyal opposition.

Also striking, however, was Cameron’s response. The prime minister swatted away Corbyn’s conciliatory gesture praising foreign minister Philip Hammond’s recent trip to Tehran and the landmark nuclear energy deal struck with Iran — by calling up an instance where Corbyn once off-handedly referred to Hamas and Hezbollah as ‘friends.’

Most striking of all is the giggling from chancellor George Osborne (pictured above), seated to the right of Cameron on the ministerial benches. Labour’s old guard is apoplectic about a Corbyn victory. Former prime minister Tony Blair has warned that Corbyn supporters should get heart transplants and are playing ‘Alice-in-Wonderland’ politics, while his successor and one-time rival, Gordon Brown, paced up and down for 45 minutes while delivering a lecture on Labour history that warned that the party must not merely be a party of protest but a party of government.

Tories, meanwhile, cannot hide their glee at a likely Corbyn victory and an even likelier Labour civil war. While Cameron has said that he will step down before the 2020 election, no one is more well-suited to succeed him than Osborne, who will benefit as the British economy continues to grow.

It’s no wonder Osborne couldn’t hide his glee.