May 5, 1951: Groan

Another chase.  I have to disagree with Charlie Brown in the last panel, that was not really all that notable a joke.

April 5, 1951: Who's on first?

Turnabout, chase, bad joke, etc.  Charlie Brown's quip this time, "Someday I'll probably drive this poor girl crazy," shows Schulz's recognition of the pattern.  It's pretty funny this time anyway.

Whose house is Patty and Charlie Brown in in this one, Patty's?  Which is it usually?  Does Charlie Brown ever go home?

EDIT: Somehow I didn't get the embed code into this one the first time. Shame, as this is one of the funnier strips I've seen yet.

January 26, 1951: Viewing them head-on

Sometimes the real humor of a strip comes from a little thing.  Here, the joke would be much less effective if it weren't for two little things: the smile on Charlie Brown's face and the annoyance of Patty, both in the last panel.  Those tip off the reader that the characters know it's a joke, and that it's kind of dumb.  Although the strip does offer a "dumb kids" joke sometimes, more common are these strips where smart kids say something dumb to entertain themselves.

I mentioned last time that the characters look more like their later-day versions when viewed from the side, with only one eye visible, than from head on or three-quarters, when both eyes are visible.  It's due, I think, to the distance between the eyes, which is fairly substantial here, and the way open mouths are depicted, with a vertical line to define the nose and mouth when we shouldn't be seeing one.

January 15, 1951: No wonder they hate Charlie Brown later

Another CB-and-Patty exchange here.  Boy, wasn't Charlie Brown something of a smart aleck back then? Maybe his later troubles are a result of negative karma build up during the first couple of years.

I think even the shaggy dog jokes from this era are saved, though, by Schulz's winning art style.  Look at Patty's "angry look" there.  So much emotion conveyed with a simple angry eyebrow and a balled fist.

January 10, 1951: The chase is on

Another example of the last-panel turnabout joke, this time involving a chase.  Be warned: a lot of these are coming up.  It's funny how this joke, about "being hot" would be considered flirtatious today.  I like the exclamation point above Patty's head in the third panel, a way to show surprise without having it register on the character's face.

The punchline from Charlie Brown, "I get my laughs," is rather meta.  The formula on this style of joke is pretty strict, and the ultimate humor relies on coming up with something for the joking character to say in reference to his motive in the last panel.  Schulz used them enough that he must have had a hard time coming up with fresh punchlines for these sequences.

January 3, 1951: Why you little!

This is the beginning of a particular strip formula that would be used a lot in these months, especially between Charlie Brown and Patty.  The first three frames present either a bad joke or one that insults one of the parties, and the fourth shows the non-joking character's reaction, usually in the form of the joking character knocked down but still mirthful, or being chased.  We'll see this pattern so many times in the upcoming strips that I should think of a name for it.

"Turnabout" strips are the best I've come up with, referring to the sudden, undepicted change of attitude between the third and fourth panels.  The punch from the formula comes from the sudden break between the last two panels.  Notice that Patty hasn't changed expression between the second and third panel of this strip, and we only see the result of her wrath in the fourth.

It's fairly amazing, really, that with all the hostility the Peanuts characters are capable of showing for each other, so much of it is understated or not shown.  It wasn't until crash of thunder Lucy showed up that a character could commonly get away with much wrath depicted directly on the page.

EDIT: fixed formatting.