This is a predecessor of Schroeder's "X days until Beethoven's birthday" gag. It's also another reference to a real-world day, in this case Halloween. The extraneous "boo" in the last panel is one of those things that's funny for no real reason. It's like he just added it as an aside.
The text of ROASTED PEANUTS is copyright 2009-2011 by John Harris. No copyright is claimed over the comic strips, which are here under the principle of fair use. Strips presented for review purposes only. We love Peanuts a whole lot, and wouldn't dream of exploiting it. Please don't sue us; we're only trying to love. Thank you for reading this notice.