Social media and the iPhone Duo subreddit are filled with reports of Apple’s foldable failing quickly and in spectacular fashion. Some users report having the phone for only a few hours before the hinge seems to catch on something, then audibly crack and break the screen. Tellingly, the cracks all seem to happen in the same place.

YouTuber CuriousHagi was able to reproduce the cracked screen during some durability testing of the iPhone Duo. Then he pulled it apart to try and find the culprit. What he found is that the Duo’s hinge is quite complex, consisting of a gear-like central hinge and two different types of linking hinges.

The piece that broke is one of the links in the middle of the phone that happens to be thinner than the links below or above it, and it snapped at a small notch where it would be weakest. He also found marks where the hinge met the support plate, indicating where it may have gotten caught.