NEW YORK — Steven Spielberg hasn't watched Schindler's List with the sound on in 25 years.

The filmmaker, 71, descended on Tribeca Film Festival Thursday night for a 25th anniversary screening of his 1993 Holocaust drama, which he last saw on mute while restoring the movie for its Blu-ray release five years ago. But Tribeca marked the first time he's seen it with an audience since it premiered a quarter century ago, winning seven Oscars (including best picture) and earning the No. 8 spot on the American Film Institute's "100 Greatest American Films of All Time" list.

Based on Thomas Keneally's historical novel Schindler's Ark, the film tells the story of the real-life Oskar Schindler (played by Liam Neeson), a German businessman who saved the lives of more than 1,200 Jews by employing them in his factories during World War II. It co-stars Sir Ben Kingsley, Caroline Goodall and Embeth Davidtz, all of whom joined Spielberg and Neeson onstage at New York's Beacon Theatre for the reunion.

The biggest takeaways from their post-screening panel:

1. Robin Williams did comedy routines to help Spielberg cope.

Filming such a gravely serious movie during the winter in Poland, Spielberg says he relied on episodes of Saturday Night Live for catharsis, as well as weekly phone calls from his dear friend and Hook star Robin Williams.

"Robin knew what I was going through, and once a week, Robin would call me on schedule and he would do 15 minutes of stand-up on the phone, and I would laugh hysterically, because I had to release so much," Spielberg said. "But the way Robin is on the telephone, he'd always hang up on the loudest, best laugh you'd give him. He'd never say goodbye, just hang up on the biggest laugh."

2. The cast experienced anti-Semitism firsthand.

Many festival-goers gasped as Spielberg shared disturbing details of anti-Semitic incidents they witnessed during filming, including swastikas painted near the set and a Polish woman who stopped actor Ralph Fiennes in his Nazi SS officer costume to say she wished "all of you were back here protecting us again," the filmmaker recalled.

Kingsley even had a shocking encounter that turned physical, after a German-speaking man approached Israeli actor Michael Schneider at a bar and asked if he was a Jew. "He mimed a noose around his neck and pulled it tight, and I stood up," Kingsley said. Added Spielberg: "You did more than stand up."

3. The visceral atmosphere on set was too much for some extras.

The concentration camp scenes were harrowing to shoot for all involved, to the point that some became physically ill. After filming the scene in which a group of Jewish women are mistakenly delivered to Auschwitz and believe they are going to be gassed, "two young actors, both Israeli, couldn't shoot the next three days," Spielberg said. "They had breakdowns after that. There was trauma everywhere. You can't fake that."

Similarly, filming the chaotic scene at the Kraków death camp when the men and women are forced to strip naked for a health examination — only to panic when their young children are transported to the gas chambers — "was probably the most traumatic day of my entire career," Spielberg added.

4. The film's emotional conclusion was a last-minute addition.

The movie ends with a poignant coda of the real-life surviving "Schindler's Jews" as they visit the late hero's grave site in Jerusalem. Spielberg came up with the idea about three quarters of the way through shooting, as a way to remind viewers that what they witnessed onscreen was based on actual events.

"I'm so known for films that are nothing like this, I didn't know that if people and the way they perceive me was enough to be able to present this movie as truth, which it was," Spielberg said. "I got really worried and it came to me, 'What if we can get as many of the Holocaust Schindler survivors and get them to put stones on Schindler's grave?' That was an idea that was never in the script — that was a desperate attempt from me to find validation from the survivors' community to certify that what we had done was credible."

5. Spielberg is prouder of Schindler's than any other movie he's made.

Reflecting on the film in the greater context of his five-decade career, "I certainly know that I have never felt since Schindler's List the kind of pride and satisfaction, and sense of real, meaningful accomplishment — I haven't felt that on any film post-Schindler's List," Spielberg said.

In response to a recent national survey tied to Holocaust Remembrance Day that suggests many Americans — particularly Millennials — have waning knowledge of the Holocaust, the director called for it to be a mandatory part of the "social-science curriculum in every public high school in this country. These stories of Holocaust survivors are necessary to tell."