The mere act of observing something can often have an impact on its behavior. In physics, this is known as the observer effect, though it could just as easily be applied to movies, as well. Watch any given film more than once, and you're bound to pick up on new details, insights, or hidden clues. With each viewing, the film takes on a new layer of meaning, reinventing and reformulating itself right before your eyes.
This is especially true of Quentin Tarantino's films, which, over time, have become notorious for their obscure references and stylistic subtleties. Take, for instance, the above screenshot from Kill Bill: Vol. 1, recently captured by Reddit user TheRobertissimo. Here, the camera captures the bottom of Uma Thurman's Onitsuka Tiger Tai Chi's as she struts her way across the House of Blue Leaves, just minutes before her epic battle against O-Ren Ishii (Lucy Liu) and her "Crazy 88" army. Tarantino only pauses here for a few seconds, but it's just long enough to make out the appropriately belligerent "FUCK U" message inscribed across the soles of Thurman's shoes.
It's a small detail, and one that has virtually zero impact on the film's narrative, but it definitely makes that 574th viewing all the more worthwhile.
The full scene is embedded below, along with an even more subtle shot of Thurman's soles from earlier in the film, as she speeds across Tokyo on her motorbike.