But it doesn't open. There's no doorknob.
3 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 00:36:24.100 in the Blu-ray version of the movie.
Quote context
[...]
- No! Please, no. I cannot be fired. I'm fired. Aaaah!
- Oh, this is heavy. What am I going to tell Jennifer?
- Oh, Doc, am I glad to see you.
- Go out the front door. I'll meet you there.
- But it doesn't open. There's no doorknob.
- Press your thumb to the plate.
- Marty, what does this fax mean?
- Oh, Mom, it's a joke, an office joke. Kind of a joke fax.
- Oh, Marty, I heard you yelling.
[...]