For the scene when Wendy is on the stairs holding the bat to defend herself against Jack, Stanley Kubrick had her do that scene 127 times for the camera. He wanted her SCARED and terrified of what her husband had become. It became so much that she finished filming the scene dehydrated and blisters on her hands from gripping the bat. What you see on the screen is not acting. That's legitimate exhaustion and horror.
To this day that remains the most takes of a single scene in movie history.