Twin Peaks spoilers:
It’s funny that I still find that scene scary, because it’s later revealed that nothing particularly terrifying was actually happening. At the time, the implication seems to be that the gloved hand belonged to the killer, that the killer had been stalking James and Donna, and that Mrs. Palmer had a creepy psychic link to him. Later it’s revealed to just be Dr. Jacoby.
But I still think the scene is extremely unsettling, mostly because of the editing (esp the ominous recurring shot of the stairs and ceiling fan, an image that usually symbolizes danger in the series), the music, and Grace Zabriskie’s acting. And the otherworldly sound design they do on her scream. The scares came rushing back to me like the first time I watched it when I saw the mirror. That little shape is Bob, the long haired evil spirit that is actually responsible for Laura’s murder and who seems to continue to hang out in the Palmer household for reasons that become clearer in season 2. You can see him for a second or two when Mrs. Palmer sits up in alarm.
Watch the scene in non-photoset form here.