Linus is the most recent character to bear that weird, slanted frown, which turns up frequently around this time.
More interesting perhaps is that this strip clearly shows how Snoopy's design has progressed. His snout is thicker, his ears clearly rise up off his head a little, he sets a better pose standing, and he seems to definitely be a larger animal than the early form of the character. He seems a bit more like a real dog here.
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