There is more than one instance where you see a poster for two missing young boys. Those boys were actually pictures of Rob Zombie and his brother (the lead singer of Powerman 5000) as children.
Most of the cutaway scenes (Otis torturing cheerleaders, Baby masturbating with the skeleton, etc.) were filmed in Rob Zombie's basement after filming wrapped. He would invite cast members over to his house on the weekends and shoot the footage himself with a 16mm hand-held camera. With the exception of the shot of a setting sun, he created the opening credits the same way.
In 2014, Rob Zombie acknowledged the movie's cult following but admitted that he himself is not fond of it. Zombie called the film "a calamitous mess [...] All I see is flaw, upon flaw, upon flaw...upon flaw".
Filmed in 2000, not released until 2003.
At one time it was reported that about forty minutes of footage was cut out of the film before Rob Zombie finished his unreleased 105 minute director's cut (final theatrical cut is 89 minutes long). Some of the known deleted scenes which were left out of his director's cut included four teenagers on their road trip before they arrive at Captain Spaulding's gas station, and more characters which were cut out completely, including more scenes with Skunk Ape who is only briefly glimpsed in final film. In 2003 Zombie spoke about releasing some extended version which would include deleted footage of scrapped characters and all uncut gore and death scenes, but no such version was ever released. Zombie's director's cut was shown once in 2003 at the Argentinian film festival which is why there are many reports of the lost scenes from that version.