Yes, there was. The post-credits scene in Scary Stories provided a hint or teaser for a potential sequel or added some additional context to the story.
One post - credits scene scary story could be about a haunted house. After the credits roll, a character goes back to the seemingly empty old house. As they enter, they hear strange whispers and see shadowy figures moving in the corners. Then, a cold hand grabs their ankle from under the bed.
They're popular because they add an extra layer of thrill. Audiences are already in the mood for something exciting after watching a movie, and a post - credits scary story catches them off - guard. It's like a little bonus that keeps the horror going.
One post - credits scary story could be about a haunted movie theater. After the credits roll, a lone janitor is left cleaning. Suddenly, he hears the sound of the projector starting up again on its own. He turns around to see the seats filled with shadowy figures that seem to be watching a movie that isn't there.
Well, they are effective because they use the context of the whole movie or viewing that just happened. You've been immersed in a certain atmosphere, and then the post - credits part subverts your expectations. It's like a final jolt of fear that stays with you. Think about it. You've been on an emotional roller - coaster during the movie, and just when you're starting to relax as the credits roll, the post - credits scary bit hits you and brings all that fear back, and sometimes even amplifies it.