This seems to be the first act of full-on spite Lucy commits that cannot be explained by familial antipathy or mere childishness. It is an act of pure evil by her, and it's glorious. Look at that little smile on her face in panel six. It's against her favorite punching dummy, too. And Charlie Brown was so happy in the throwaway panels!
We even get that "down on his luck" slanted mouth in the last panel.
Schulz had many, many positive attributes as a cartoonist, but there are a couple of things in these early days he could have used some improvement on. One of them was in varying his phrasing; here, Lucy uses the "slaughter" line twice, which is a bit awkward. This isn't the only strip in which this defect can be seen. As Schulz gains experience writing dialogue I believe these errors eventually go away.
