Subtle tics and quirks are an easy way for filmmakers and actors to make their characters feel truly alive rather than simply props for the sake of telling a story.
And while character traits are usually obviously laid out for the audience to easily digest - say, Tony Stark's (Robert Downey Jr.) fondness for eating in the middle of a conversation - sometimes directors can imbue their films with a more impressively low-key brand of character development.
These 10 films, all terrific works in their own right with brilliantly defined characters, nevertheless dared to take things a step further by rewarding those few audience members who really paid close attention.
It's entirely possible to watch these movies dozens of times and never pick up on these below-the-radar character flourishes, adding inessential yet undeniably intriguing shade to characters you're probably already huge fans of.
And so, we're left to wonder how many other minor character bombshells are sat out there just waiting to be discovered in cinema's all-time great films...
10. Elastigirl Speaks Out The Right Side Of Her Mouth (Just Like Holly Hunter) - The Incredibles
The Incredibles' Elastigirl is of course voiced by the brilliant Holly Hunter, whose distinctive drawl is a perfect fit for the series' stretchy superheroine.
But Hunter's recognisable twang is actually a by-product of her tendency to speak from the right side of her mouth, due to a childhood case of the mumps rendering her deaf in her left ear.
Brilliantly, Pixar actually decided to incorporate this physical aspect of Hunter's vocal performance into Elastigirl herself, and so those who pay close attention will notice that Helen Parr is animated to speak from the right side of her mouth.
It's easy to completely ignore this if you're well-accustomed to Hunter's voice, but it's yet another incredible testament to Pixar's ludicrous attention-to-detail.