Don't underestimate the eagle-eyed sight of some fans.
They are extremely good at spotting some of the hardest to find mistakes in film and television, that not even the filmmakers spotted. Remember Daenerys' Starbucks coffee cup or Bran's water bottle behind his foot in Game of Thrones? How about the newest famous mistake; the "Jeans Guy" spotted in The Mandalorian? There are just too many mistakes, we could go on and on.
But some of the mistakes that fans find are crazy and will make your eyes water from starring so much to catch them. We all know that sometimes even the littlest inaccuracies crop up, but does it really matter when a little thing is out of place between shots? Sometimes there are obvious mistakes but blink and you might not even catch those either.
Either you have an eagle eye and catch them immediately or you watch something a million times and then figure them out. It only took us 20 years of watching Harry Potter and the Sorcerer's Stone, to see the Hagrid robot that replaces Robbie Coltrane in some shots. Now we can't unsee it.
Speaking of Harry Potter, that's another franchise that has a group of eagle-eyed fans that won't miss anything. Not even a little hair out of place or a simple change of shirt... or a little battle pack goes unnoticed.
The Battery Packs Were One Of The More Obvious Mistakes
There are countless mistakes that have been found in the Harry Potter films over the years. Some of the most famous happen in some of the quickest scenes too. Blink and you'll miss Hermione's towel change in Goblet of Fire, Ron's different trunks in Chamber of Secrets, Harry's shirt change in Order of the Phoenix, and the very obvious cameraman in the background during Harry and Malfoy's duel in Chamber of Secrets.
We could go on. Ever notice how Harry's wounds often change or disappear, or how there's no glass in some of his glasses. Or how about the little piece of hair that peeks out of Professor Quirrell's turban or the slight movement that Griphooks pillow in the same shot. We didn't notice any of these until someone pointed them out years later.
One mistake that's a little more obvious to us is the battery pack scene. Battery packs are of course used a lot in filmmaking. A lot of times, an actor or actress will have a battery pack, usually discreetly attached to their person somewhere safe, to power microphones, if the space is hard to record sound. Battery packs also minimize the use of power outlets and therefore reduce wires onset, which could be harmful to everyone who could possibly trip over them. Basically, they are a godsend for outdoor scenes.
Especially in scenes on the grounds of Hogwarts.
That being said, it's crazy that no one on the editing team at Warner Bros. noticed how visible Daniel Radcliffe and Emma Watson's battery packs were in one scene of Prisoner of Azkaban.
You can see them clear as day in the scene where Harry and Hermione have traveled back in time to save Buckbeak and Sirius. They get down to Hagrid's hut, hide behind the giant pumpkins and get the attention of their past selves before Dumbledore and Fudge catch them. Our first glimpse of the battery packs happens during this scene. They are kinda off to the side, and you can see that they are trying to angle their bodies in a certain way so as to hide them at the very beginning of the video below.
Then when the other Harry, Ron, and Hermione leave, we see the packs even more distinctly after they return to hide behind the pumpkins to talk about how to free Buckbeak. You can see the shape of Watson's battery pack very clearly at mark 2:23 in the video.
Then you can see the bump of Radcliffe's pack when he goes to quietly release Buckbeak from his chains at mark 2:29, and even more clearly at mark 2:36. Then they magically disappear in the next shot.
The battery packs are probably one of the more famous mistakes in Harry Potter so everyone who worked on the film, including the editors who missed them and the higher-ups, probably know they're there by now. Only we don't think they have the luxury of erasing their mistakes that the makers of Game of Thrones had when the internet was blowing up about Daenerys' Starbucks cup. They went back and completely edited it out but the only way those battery packs will disappear is if they go back and do it for a re-release of the film. That's almost as hard as a Vanishing spell.