The .mp4.mp4 naming convention is a common tactic used in file-sharing communities. It often serves two purposes:
After a few seconds of silence or low-level noise, the video abruptly cuts to a high-contrast, disturbing image—often a distorted face or a "creepypasta" character like Jeff the Killer or a "void" meme. 8095749.mp4.mp4
You likely just experienced a jump-scare. the second extension might be hidden
In some interface views, the second extension might be hidden, making it look like a standard video file while signaling to "those in the know" that it is a specific, often edited or corrupted, troll file. often edited or corrupted