It should be explained for anybody doesn't know who Charlotte Braun. She was a girl that came into Peanuts as a counterpart of Charlie Brown. That role was taken by Sally eventually. Her habit of talking loudly was eventually taken by Lucy. But since the character wasn't very developed, Schulz decided to drop the character. In 2000, it was discovered that there was a letter written in 1955 by a reader who disliked the character, which was responded by Schulz saying that he was already planning to discontinue her. He reminded the reader and her friends that they would have the death of an innocent child on their conscience, and would they be prepared to accept such responsibility? At the end of the letter there was a picture of Charlotte Braun with an ax in her head. Her strips were never reprinted until they came out with The Complete Peanuts second volume, which Mort is reading there. Oh ya one more thing. Mort is back! Haven't seen him since July.

Here's the ref for it. [link] Wikipedia is your friend.