What does Snoopy mean by "WHEN will I ever learn?!" At first glance it looks like he's expressing regret that he enjoyed himself too much and, in his excitement, hit the pavement. But look at Patty and Violet's faces: they don't smile, or frown, or act even act surprised the whole time. Even in panel six their expressions are remarkably deadpan. In panels eight and nine their reaction is mostly: "Well, that happened. Lemonade?" Because of this, I propose that Snoopy's thought balloon in the last panel has more to do with disappointment at the lack of concern expressed by the human girls than any regret for going overboard.
Oh, also, this is Snoopy using thought balloons completely in the modern style, with a trail of bubbles as if talking to himself. I don't think it's absolutely the first time it's happened, but up until now, except for one or two early instances, he's either been completely wordless or used word balloons. That marks a major advancement for the strip.
