Also, not the first time Buck has died in a doorway of head trauma. Heck, given how big a fan Tarantino is of Battle Royale, even the famous yellow track suit could be taken as a shout-out to Chiaki Kuriyama's role in that movie.
Science Marches On: The MythBusters tested as to whether it's really possible for a person to punch their way out of a coffin buried deep underground, with the conclusion that it isn't: even the world's most skilled boxer wouldn't be able to punch a hole with that little space for drawing the fist back to create enough force, and before they'd manage to create a crack the air would have run out anyway. And even if a person did manage to punch through, they would immediately be buried and suffocated in dirt.
Tarantino originally intended it to be one long movie, with an intermission.
In the original script, Gogo was a pair of Creepy Twins: The silent one at O-Ren's side and the Ax-Crazy one at the bar. After the quiet one (Gogo) is killed, the crazy one (Yuki) stalks The Bride all the way to Pasadena (that's her in the ice cream truck in Vol. 1). Yuki takes some ultra-steroids that Bill's cooked up and goes after The Bride with guns and bombs and blows up the Pussy Wagon in the process, but dies of an overdose before killing her. The Bride is so shaken that she calls Hanzo for reassurance and then calls a certain Nurse Bonnie to fix her up. Bonnie is hysterical and claims she "got out of that a long time ago," but like Hanzo is ultimately not immune to The Bride's charms. This is still referenced in the final cut: when the Bride meets Esteban in a convertible, he says that Bill said she would be driving a truck. She simply replies that her "Pussy Wagon died on her." There's also the Narm-ish variation of The Bride confronting Bill in a wedding dress for their final showdown.
There are rumors that the original script called for Beatrix kill O-Ren via decapitation (which would have been a Karmic Death for O-Ren, given how often she killed people that way). It was scrapped because that would have made O-Ren's dying words - recanting her previous refusal to believe that the sword was an authentic Hanzō sword - impossible.
Warren Beatty was who Tarantino had envisioned as Bill. Michael Madsen was originally going to play Johnny Mo.
In one version of the script for Volume II, Pai Mei's lips would be speaking Cantonese while his voice (dubbed by Tarantino) would be in English, imitating a bad dub job.