Why? All you have to do is slip the letter into the mail slot in the front door of the house.
9 seconds sound clip from the Happy New Year, Charlie Brown! movie soundboard.
You can hear this line at 00:12:31.418 in the VHS version of the movie.
Quote context
[...]
- Well, as a matter of fact, I'm only on Page 5 of my book.
- Come on, Chuck. Remember, you have to invite somebody.
- Well, I suppose you're right.
- I wonder if that little red-haired girl would go with me.
- What?
- Why? All you have to do is slip the letter into the mail slot in the front door of the house.
- But what if my hand gets caught in the mail slot?
- That's ridiculous, Charlie Brown.
- Charlie Brown, you worry about the most impossible things.
[...]