What trivia or anecdote about one particular movie or several movies do you find most intriguing?

Two random ones come to mind...

First, many know actor R. Lee Ermey for his iconic role as drill sergeant Hartmann in Stanly Kubrick's "Full Metal Jacket."  Ermey, however, was not originally supposed to be in the movie but was instead hired by Kubrick as a consultant (Ermey was a real life Vietnam veteran and former drill sergeant).

Early in production, Ermey expressed his dissatisfaction with the actors' performances to Kubrick during a break. Known for an ego that matched the size of his directorial talents, Kubrick sat in his chair and nodded in a disinterested manner while looking through some paperwork.

Ermey, not liking Kubrick's condescending attitude suddenly shouted "GET ON YOUR FEET WHEN I'M TALKING TO YOU!".  The assembled cast and crew gasped in shock....not only because of Ermey's outburst but because Kubrick leapt to his feet in an instinctive, military "attention" stance.

Surprised by his own reaction, Kubrick chuckled, and gave Ermey the role on the spot...

Second, while making a documentary about the original "Planet of the Apes" movies, a filmmaker noticed something interesting while reviewing hours and hours of "behind the scenes" footage:

During breaks, the actors tended to congregate in groups according to their costumed "class."  Actors dressed as Orangutans hung out with other actors dressed as Orangutans...Actors dressed as Chimpanzees hung out with other actors dressed as Chimpanzees and so on...

Even more interesting was how the movie's class structure was instinctively enforced during meal times.  The Orangutans (who in the movie are the elites) sat at the highest tables and closest to the buffet....the Apes (who were the movie "enforcers" sat around them...the Chimps (who were the movie's worker class) took the tables furthest from the food.

Curious, the filmmaker reviewed footage from his other past films and noticed the self-segregation repeated itself... In Westerns, actors dressed as "cowboys" tended to dine separately from those dressed as "Indians"... in Depression-era gangster films, actors dressed in "fancy" clothes dined apart from those dressed as "street people."

The most interesting part was that this self-segregation often trumped real-world differences.  On the "Apes" set, for example lead actors dressed as Orangutans hung out with extras dressed as Orangutans as opposed to other lead actors... 

Something to think about when considering the roots of prejudice and the subtle way we often reinforce it even when we think we're combatting it...