THINGS THAT SCARED ME WHEN I WAS A KID #4: The Cover of Creepy #62
Poe's "The Black Cat". Not only is the lady in the wall dead, but she's making some sort of hideous, soundless, accusatory shriek. And she got spittle trails in her mouth. And her husband (who killed her) is clearly insane. And it's the kind of insanity that doesn't get better!