I'm at one of those points again where I feel like I need to link every strip. It's because this is such a formative period in Peanuts history. Many of the things we've seen frequently in later strips and compilations got their start in this period.
Here, it's the team of Schroeder and Snoopy. Snoopy works well with many characters, but Schroeder most teams only with him or Lucy. Up to this point we've also seen him and Charlie Brown in the strips where Charlie Brown draws a cartoon, and the two sometimes meet on the pitchers' mound.
It might be interesting to do a statistical analysis of which characters appear with which other ones, in what frequency. I'm not gonna do it, though.
I'm not sure, but this might be the first time we've seen a single 'Z' in a word balloon used to signify sleep. Later on Schulz has some fun with this convention, especially with giant, serif'd Zs.