The scene doesn't frighten anymore, but 1925 filmgoers were shocked at Lon Chaney, Sr.'s on-screen visage. Visual images and stills were tightly controlled in those days, so most everyone only heard about the scene before seeing it.
The comment thread under that video got me to thinking. Excerpt:
Comment: I cant help but laugh at those old movies, their acting is so over-the-top!
Reply: Back then, theatre (which was pretty over-the-top until Constantine Stanislavsky came along and explored naturalism in acting) was all anyone knew. Not only was the acting 'over-the-top,' the filming was very 'stagey.'I had to google Constantine Stanislavsky and I learned something new.
Chaney's parents were both deaf-mutes and he grew up with sign language as his "mother tongue." He didn't even learn to speak until he was old enough for school, even though there was nothing wrong with his speech or hearing. Later, his mother fell ill and young Chaney was left to care for her after she lost the use of her hands. They communicated with facial expressions. That explains why Chaney was so unique as Hollywood's first character actor. He was a skilled make-up artist as well. But Chaney did not make the transition to "talkies" -- he died of a throat hemorrhage in 1929.
[added] Here is the original trailer. Also, 15-year old Carla Laemmle had a minor role in the film and she's still alive at age 104!
[added] Sadly, she passed away ten days after I wrote this.