Asked by a Reuters reporter how it felt to be in Venice, Liam replied: "Biblical man, biblical".
Noel opted for a more Italian response: "Bellissimo."
Later, Liam appeared less impressed by photographers yelling for attention.
"Why all the shouting? Is this what you do at the Venice Film Festival? Scream at people?" he asked.
Oasis, the Manchester band whose anthems helped define the 1990s before feuding between the two brothers tore it apart, reunited last year for a tour across the United Kingdom, Ireland, North and South America, Asia and Australia.
The documentary Oasis: Don't Look Back in Anger follows the gradual repair of one of music's most famous fractured relationships over weeks of rehearsal and months on the road.
"You sort of saw that reconciliation happen on stage in front of the world," said Dylan Southern, who directed the film alongside Will Lovelace.
The thaw takes time.
When Liam arrives for his first rehearsal he doesn't acknowledge anyone around him before leaving abruptly without saying goodbye.
Underscoring their mutual animosity, Noel reveals that their respective children had never met before the reunion tour but swiftly went on to become great friends.
At the end of the film, Noel describes Liam as "delightful" - something he admits he had never expected to hear himself say.
The filmmakers said they deliberately avoided interfering, keeping themselves largely invisible during the lengthy practice sessions and allowing events to unfold naturally.
As shooting moved into the concert stadiums, Southern said the focus widened to include the fans whose affection became an integral part of the brothers' rapprochement.
Steven Knight, who wrote the script, said the filmmakers had no way of knowing whether the reunion would succeed but always hoped the story would become one of forgiveness.
"From the beginning, we wanted to make this a film about reconciliation, redemption and forgiveness," he said, adding that neither Gallagher was likely to express emotion openly.
"They're British working-class men, so they're not going to high-five or hug or cry," he said.
Knight, who is writing the script for the next James Bond film, said the real-life story of the Oasis tour proved more compelling than anything he could have scripted.
"This is better than any fiction that you could write," he said.
Southern chipped in: "And no one could play Liam Gallagher except Liam Gallagher."
The film is being shown out of competition at the Venice Film Festival, which runs until September 12.
