Look at Patty in the distance in panel 2. Would someone only familar with Peanuts' later days recognize her as being a Charles Schulz character? But the design, as opposed to many other comics of the time, is unquestionably modern; you could probably find a recent illustrated children's book out there somewhere with a character that looks like Original Patty.
Also in this one, we see the cartoon shorthand of showing anger with a word balloon containing a scribble. The scribble of shame.
