LONDON • Was it the emphatic way that Martin Skrtel, from a corner by Adam Lallana, volleyed in for 4-1? Was it the Liverpool players hurdling the hoardings to leap into their giddy support? Was it Juergen Klopp bear-hugging his assistant, Zeljko Buvac? Or seeing even Dejan Lovren playing well?
This was in the home of the Premier League title favourites Manchester City. That home was devastated, ransacked on Saturday.
Barely six weeks into Klopp's reign, English football club Liverpool are unrecognisable from the timid crew he took control of. You know momentum when you see it, and the only question from the stunning win seemed which moment best expressed the new confidence.
•Manchester City conceded three goals in the first half of a competitive game at the Etihad Stadium for just the second time, following their 2-3 loss to Manchester United in the FA Cup in January 2012
•City conceded four goals in a competitive game at the Etihad for the second time, following their 2-4 loss to Aston Villa in the League Cup in September 2012
•It is the first time City conceded four goals at home in the Premier League since February 2003 - a game against Arsenal at Maine Road that ended 5-1
•Sergio Aguero (85 goals) is the top-scoring South American player in the EPL
•Liverpool have scored as many goals in their last two away Premier League games (seven) as they managed in their 11 before that.
City also raised questions, but not the flattering sort. How could a team supposedly this season's best be thrashed to such an extent? This could have been 5-1, 6-1, perhaps 7-2.
And how could Manuel Pellegrini get it so wrong, once again, against opponents who quicken a game's pace? Young, fast Tottenham Hotspur embarrassed City in a similar way in September, also 4-1.
Starting with just two in midfield was one Pellegrini crime and though he tried to rectify by hauling Yaya Toure, his captain, off, to introduce Fernandinho and Fabian Delph at half-time, it changed little.
His centre-back pairing was completely wrong: Elaquim Mangala and Martin Demichelis were overrun by a brilliant Brazilian tandem of Philippe Coutinho and Roberto Firmino. And what does he continue to see in winger Jesus Navas?
As a side, City are artistic, but their fault is wanting to fill the canvas with leisurely brushstrokes, in their own time. Their sluggish build-up was targeted by Liverpool.
We are learning about Klopp, that gegenpressing is as much focused as it is frantic. What a job his players did at picking out the slow and weak in Pellegrini's pack - and pouncing.
Mostly it was the defenders. Mangala, Bacary Sagna, Demichelis, Aleksandar Kolarov; none have quick feet, none are as smooth in possession as perhaps players of a very top side should be.
Poor Mangala, for one, must have gone to bed with Firmino and Coutinho buzzing in his head.
Perhaps the greatest compliment that can be paid to Liverpool is they played the kind of thrilling football that City's owners in Abu Dhabi want to see of their own team. Modern-day City have never been beaten so heavily in their 12 years at this ground.
Liverpool were three ahead after 33 minutes and could conceivably have scored that many again before Sergio Aguero's goal, on his return from injury, briefly offered City a flicker of hope before half-time.
Coutinho, in particular, was exhilarating, scoring one and playing a significant part in two others. Firmino had his best game for the club and it was almost a surprise Liverpool restricted themselves to only one more goal in the second half, courtesy of Skrtel's 81st-minute shot.
James Milner, one of several outstanding performers, will have cherished his return to his former club, putting in an indefatigable shift, and Emre Can played with great distinction.
Raheem Sterling, in stark contrast, had a difficult game against his old team-mates, culminating in him completely missing the ball with the goal at his mercy.
Joe Hart was partly to blame for the third goal, but his team-mates ought to be grateful that his goalkeeping prevented the ordeal being even worse for City.
THE TIMES, LONDON, THE GUARDIAN, AGENCE FRANCE-PRESSE