The visual jump-scare is accompanied by an extremely loud, distorted screech or "earrape" audio track intended to shock the listener. Why the Double Extension?
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.
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.
You likely just experienced a jump-scare.
While the video itself is generally just a prank intended to scare you, files shared with double extensions can sometimes be used to disguise malicious scripts (e.g., filename.mp4.exe ).