After each of Lionel Messi's quartet last night it felt obligatory. The Nou Camp needed to know if what they had just witnessed really was as good as it seemed. It was. Each time the gasp that came was deafening.
This was both magic and real. Which just about summed up Barcelona last night. They combined energy and discipline with the feathery touches of Messi and Xavi that lift the team apparently effortlessly to another level.
It is a level that Arsene Wenger described before the first leg as 'art'. After that vivid display in north London, one that made Wenger and his players shudder at their own limitations, Wenger added of his squad: 'The impression was deeper on the players than it should have been.'
The heir to Maradona: Messi caps a phenomenal display with his fourth of the night
How could it not be? If Messi is entering the territory where comparisons with a true great such as Diego Maradona feel justifiable and Xavi is building a case to be seen as an heir to Zinedine Zidane, then the Barcelona collective are deserving of all the favourable reviews coming their way.
Those statistics we are continually being fed have their power reduced by their sheer number but a week ago the fact that Barca had 71 per cent of possession in the first half made us wonder aloud.
Here Barca had slipped to 69 per cent, which coach Pep Guardiola might mention one day, but over the two legs Barca made in excess of 1,300 passes. It is a beautifulform of torture they purvey.
'Here I am,' says Xavi. 'Now I'm over here. Now here.' At times Arsenal must have felt like they were chasing ghosts. But it is reality.
In reality Barcelona are this good. They will surely be confirmed as great on May 22nd in the Bernabeu Stadium, Madrid when becoming the first team of the Champions League era to successfully defend their title.
Guardiola takes his players there on Saturday night in La Liga, so Real Madrid must have watched this and blown out their cheeks in despair.
Imagine how Arsenal felt. This is a massive pitch area as well as a monument of a ground. A temptation for lesser mortals would be to bring in the touchlines or to launchit long. Instead Barca play five-aside retention football, constantly shifting the smaller game in their heads across and around the pitch.
At least Arsenal had a plan to disrupt it all.
They would wait, counter, then make the occasional charge. And it worked. Once. When Abou Diaby rushed onto Gabriel Milito in the 19th minute, Barca were wrongfooted and Nicolas Bendtner had made the tie 3-2.
It was the only time in three hours that Arsenal were ahead and their advantage lasted three minutes.
At a stretch: Bendtner puts Arsenal ahead on the night ' but not for long
Messi was aroused. Apparently he'd been quiet in the first leg. Now he was a riot.
Each of his three goals in that devastating first-half 21 minutes was worthy of a frame on Wenger's wall at home.
Comparisons are all the rage and the first goal tore into the net with the venom of German powerhouse Gunter Netzer. But the next three, we can say, were pure Messi.
Admittedly he will face more certain central defences than Arsenal's Jose Mourinho will already have started his counter-intelligence for what is a mouth-watering semi-final against Inter Milan.
Last night, Mikael Silvestre's inadvertent one-two with Messi for the equaliser reminded you that William Gallas was missing. Gallas, Cesc Fabregas, Robin van Persie and Alex Song: they would have made a difference here.
But Barca were also missing key men and we've been told for a long time that it is a squad game now. How strong does Arsenal's squad feel after a chastening experience such as this?
They had Sol Campbell on the bench alongside Craig Eastmond. Even without Puyol, Pique and Ibrahimovic in the squad, Barca had Andres Iniesta, Yaya Toure and Thierry Henry among their substitutes.
One reaction would be to say Arsenal are shallow.
But at a time of comparisons, that is too hasty. It ignores the fact that Barcelona have assembled a special crop of players first under Frank Rijkaard, now underGuardiola.
All eyes on me: Barcelona bundle the magical Messi before the assembled media
But there remains the issue of how Wenger elevates his squad try and get closer to the Catalans.
Barca are not shy when it comes to investment look at Ibrahimovic and there will surely be pressure from the Arsenal faithful for Wenger to go to market this summer.
'We have to add something, for sure,' admitted the manager afterwards, but he said he would not be buying a new centre-half tomorrow.
Arsenal need one for August. By then the Bordeaux striker Marouane Chamakh should be in the squad, although they surely require more than a couple of new faces.
Wenger knows economics as well as art appreciation. Should they return here next season in the Champions League, he will want those screens to be replayingArsenal goals in front of a silenced crowd.
For now, though, Barcelona are the big noise and Lionel Messi is the main thrill.
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