Maybe it's the theme music.
Zadok's The Priest sounds as sweet as any other piece of music you will hear on a Champions League night.
Being under the lights at Parkhead in Europe's premier competition does something to the Celtic players and supporters alike. It also does things to opposition players.
Franz Beckenbauer, Gianluigi Buffon, Cristiano Ronaldo, Samuel Eto'o, Zlatan Ibrahimovic, Carles Puyol, Steven Gerrard, Owen Hargreaves, Carles Puyol, Michael Owen, Clarence Seedorf, Karl-Heinz Rummenigge, Frank de Boer, Stan Collymore, Michel Platini, Wayne Rooney, Gerard Pique, Sven-Goran Eriksson, Oliver Kahn, Xavi, Iniesta, Dani Alves, Benni McCarthy, Sepp Blatter, Lennart Johansson, Claudio Ranieri, Jose Mourinho and Pep Guardiola... to name but a few.
Football's glitterati have all lined up to heap praise on the rarified atmosphere provided by the Hoops fans on a European Cup or Champions League night.
Uplifting. Inspiring. Intimidating. Awesome.
It's multiple-choice answer E: all of the above.
There is no football place on earth like Celtic Park on a European night.
Former Manchester United boss Sir Alex Ferguson once famously remarked: "Anyone going to Celtic Park now is saying 'You've got to beat that atmosphere, the energy they spend in their games'."
“There is perhaps no greater home-pitch advantage in all of football than a Celtic home match at Parkhead," wrote Marca, the renowned daily sports newspaper in Spain after the Hoops humbled mighty Barcelona in 2012.
It will be this new and life-affirming experience waiting for Celtic boss Ange Postecoglou and his team when they line up inside the amphitheatre they call Paradise in Glasgow's east end a few weeks from now.
Brazilian superstar Juninho Pernambucano experienced it all for himself first-hand nearly two decades ago.
The former Lyon midfielder was a dead-ball specialist and noted for his bending free-kicks. It was he who developed the 'knuckleball' technique and he still holds the record for the highest number of career goals (74) scored directly from free-kicks. He is widely considered by many to be the greatest taker of all time.
Speaking exclusively to The Celtic Way Juninho - who became the sporting director at Lyon after retiring - insists he has nothing but fond memories from his jousts with Martin O'Neill's side in the 2003-04 Champions League group stages.
The French side succumbed to a 2-0 loss inside Fortress Parkhead courtesy of goals by Liam Miller and Chris Sutton.
Miller's headed opening goal in particular, which was a free-flowing and passing team move, had former Luton Town boss turned ITV co-commentator David Pleat in raptures.
Juninho admitted to being blown away by the Celtic supporters in Glasgow that night. So much so that they reminded him of the football-crazy fans in his native Brazil.
"The first time I went to Scotland, it was to face Celtic," Juninho told The Celtic Way. "I tell you one thing, never in my life have I forgotten what the experience was like.
"What energy the Celtic team and their supporters had. They fed off each other. We in Brazil are sometimes taught to think that there are only strong and passionate fans in our country. Of course, Brazil also has strong and passionate fans - but that night I saw something amazing.
"Altogether the Celtic fans were singing all the time, non-stop. They were so passionate. When the first half ended, on the return to the field, it looked like the game was still going to start because they started singing again as they had in the beginning. It made the hairs on the back of your neck stand up. It was breathtaking.
"Lyon lost the game 2-0 to Celtic but the experience was fantastic. The Celtic crowd and the atmosphere inside the stadium is something I have never forgotten, honestly. I thought the crowd in Glasgow was impressive."
However, Juninho and company would gain ample revenge in the return leg in the corresponding fixture as Celtic controversially exited the tournament behind a Juninho brace.
Ironically it was Juninho's hotly-contested penalty five minutes from time which was awarded by Swiss referee Urs Meier for handball against Hoops defender Bobo Balde which condemned Celtic to a 3-2 defeat.
The now 47-year-old can't wait to welcome Celtic back into European football's premier club tournament.
He insists that Celtic boss Postecoglou and his team should embrace the whole Champions League experience and, crucially, dedicate any success in the tournament to their wonderful supporters.
The 40-cap Brazil international reckons that whoever is drawn in Celtic's Champions League group will have the pleasure of taking part in something special.
"Whoever is in the Celtic group will have the privilege of seeing it all up close and personal," he said. "Good luck to Celtic and their fans in this very important group stage. I wish them well.
"It is good to see a club like this back competing at this level in the Champions League. They are one of the most renowned and famous names in European football because the club won the European Cup."
Juninho, in fact, is adamant that the Champions League would cease to exist as a spectacle if it weren't for the football fans of the top European clubs.
"Deep down, football is for the fans," he insists. "We play for them and it is the fans who make the players money and not the other way around.
"In addition to going to the stadiums, the supporters give the audience that makes the TV stations pay the amounts that are currently paid. So it all starts with the supporters. If the players do not understand this, then they will never become great footballers.
"Fans support football, that's the truth. The party without them would never be any fun. That's why I always say that the player who understands this will usually reach his best in his career, play the best he can and will have no regrets."
It's five years since Celtic last competed in the Champions League group stages and finished third in a group comprising Paris Saint-Germain, Bayern Munich and Anderlecht.
Postecoglou's side have worked so hard to regain a place among European football's elite clubs.
Maybe it is time for them to write a new and illustrious European chapter in the club's history.
If the 'we never stop' mantra rings true, then Juninho is right.
No matter who they are drawn to face in the group stages, Postecoglou and his Celtic players will leave it all out there in the Champions League.
They will have no regrets.
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