Be My Valentine, Charlie Brown (1975)

Continuity mistake: As the animated film opens, Charlie Brown's mailbox has a small red flag that is attached to the rear of the mailbox with the flag facing up. At the end of the film, the flag is attached near the front of the box and it is facing down.

Continuity mistake: When Schroeder is playing the piano, Lucy is holding her book with her left hand, but in the next shot she is holding with book with both hands.

Lucy van Pelt: What are you doing, Charlie Brown?
Charlie Brown: I'm waiting for valentines.
Lucy van Pelt: Oh, well. Good luck.
Charlie Brown: Thank you.
Lucy van Pelt: You'll need it.
Charlie Brown: You didn't have to say that!

Violet: Charlie Brown, we've been feeling awfully guilty about not giving you a valentine this year. Here, I've erased my name from this one. I'd like you to have it.
Schroeder: Hold on there! What do you think you're doing? Who do you think you are? Where were you yesterday when everyone else was giving out valentines? Is kindness and thoughtfulness something you can make retroactive? Don't you think he has any feelings? You and your friends are the most thoughtless bunch I've ever known. You don't care *anything* about Charlie Brown! You just hate to feel guilty! And now you have the nerve to come around one day later and offer him a used valentine just to ease your conscience! Well let me tell you something: Charlie Brown doesn't need your...
Charlie Brown: Don't listen to him! I'll take it!

Schroeder: Well, that's it. Happy Valentine's Day, everybody. Refreshments will be served in the back.
Charlie Brown: Are you sure there's none for me?
Schroeder: Yep, none.