Last week, fastidious Netflix viewers found a scene from Friends in which Rachel is played by a stand-in actress instead of Jennifer Aniston. People were weirded out, to say the least, to see such an iconic character being portrayed — even if just for a split second — by someone other than the famous actress who was paid millions to do so. Now, another eagle-eyed fan of the beloved show has discovered a similar occurrence with Monica (usually played by Courteney Cox).Friends is one of the most popular shows of all time and was being re-watched by fans plenty before it came to Instant Netflix. Plus, it was a hit when it was on the air, with high-profile stars and tons of viewers. We've had a couple of decades to spot these gaffes. So why hasn't anyone noticed these randos until now? Is it witchcraft? A mass conspiracy? Is Netflix just messing with us?Well, mystery solved — and it's a lot more math than magic. A smartypants over at HelloGiggles has figured it out: Friends was filmed back in the '90s, before the ubiquity of the wide-screen, and the standard aspect ratio for TV and film was 4:3. Nowadays, the wider aspect ratio of 16:9 has become standardized. When the series was put on Netflix, that original aspect ratio was changed to wide-screen. So viewers are now seeing a wider angle of the show for the first time, which is how these errors are becoming revealed.We're sure people are going to be combing all 200-plus episodes of Friends for more examples of mix-ups; at least now you can be the intelligent friend and tell everybody why. "Duh, guys! Aspect ratios!"