Based on the novel "Spaceman of Bohemia" by Czech author Jaroslav Kalfar, the film follows Jakub (Sandler) as a year-long solo journey to a purple interstellar cloud takes its toll on his mental health and his marriage to Carey Mulligan's Lenka until Hanus, a big spider voiced by Paul Dano, suddenly appears.
"We got deep together, I felt pain, he (Hanus) helped me try to get out of that pain," Sandler, who is at the festival for the first time, told journalists at a news conference punctuated by laughter as he gave a ribbing to them and the other actors.
"This is a true story: When I got out of my car (in Berlin) and everyone was screaming hellos to us and taking pictures, I noticed when Paul got out, there was a group of like 400 spiders that were going 'Paulie! You're the man!'" said Sandler, who made a name for himself with comedies in the late 1990s.
The 57-year-old actor and comedian said that the wire work required to look weightless was particularly difficult.
"My body's not the most flexible body," he explained, adding: "The stunt men who would wire me up every day, I would say, 'Oh that hurts,' and they didn't believe me."
Hanus, named after the Czech clockmaker who in legend was behind Prague's Astronomical Clock, is an ancient spider who has travelled through galaxies when he encounters the relatively young cosmonaut, said Dano, known for "Little Miss Sunshine."
"If you've accrued that much wisdom, it felt something sort of Zen-like and gentle," he said in explaining his approach.
For the Oscar-nominated Mulligan, the interactions with Hanus helped Jakub to focus on the important things in life, like love and connection, in a similar way to being on one's deathbed. "If we could all have a little friendly spider tell us that, wouldn't that be wonderful, you know?" she said.
