I think it is just juxtaposing the sublime and the banal, the magical and the workaday. Presented with a glorious sight of free horses splashing along ‘twixt land and sea, instead of being inspired to flights of poesy the only thing our dullard heroes can think of discussing is restocking store-cupboard basics (oatmeal/oats being horse feed).
It’s like gazing upon the vasty deeps of the heavens filled with twinkling stars and being reminded only that you forgot to shake the dandruff out of your black velvet top. No doubt other examples occur.
“So the mention of oatmeal in particular (as opposed to, say, eggs) is an association from oats being traditional horse feed?”
That makes more sense than my first thought. I assumed the horses were pooping off-panel and horse-poop reminded her of fiber in her diet. I think I’ve been reading too many web comics where vulgarities for minor shock value are the norm.
But the joke is the same– the sublime reminding one of the the banal. But horse=>oats makes more sense then horse=>s###=>fiber=> oats
Oats as horse food (and no other interpretation) occurred to me in part because Samuel Johnson, in his 265-yo dictionary, “defined oats as ‘a grain, which in England is generally given to horses, but in Scotland supports the people'”.
Comics I Don't Understand 
I think it is just juxtaposing the sublime and the banal, the magical and the workaday. Presented with a glorious sight of free horses splashing along ‘twixt land and sea, instead of being inspired to flights of poesy the only thing our dullard heroes can think of discussing is restocking store-cupboard basics (oatmeal/oats being horse feed).
It’s like gazing upon the vasty deeps of the heavens filled with twinkling stars and being reminded only that you forgot to shake the dandruff out of your black velvet top. No doubt other examples occur.
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narmitaj got it in one.
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So the mention of oatmeal in particular (as opposed to, say, eggs) is an association from oats being traditional horse feed?
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Dana, that was my first thought as well.
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“So the mention of oatmeal in particular (as opposed to, say, eggs) is an association from oats being traditional horse feed?”
That makes more sense than my first thought. I assumed the horses were pooping off-panel and horse-poop reminded her of fiber in her diet. I think I’ve been reading too many web comics where vulgarities for minor shock value are the norm.
But the joke is the same– the sublime reminding one of the the banal. But horse=>oats makes more sense then horse=>s###=>fiber=> oats
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Woozy’s alternate reading did occur to me at one point also. But I was able to rear back, whinny, and shake my head and forelegs to get rid of it.
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Oats as horse food (and no other interpretation) occurred to me in part because Samuel Johnson, in his 265-yo dictionary, “defined oats as ‘a grain, which in England is generally given to horses, but in Scotland supports the people'”.
https://www.mentalfloss.com/article/538473/funny-definitions-from-dictionary-of-the-english-language-samuel-johnson
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And some unknown Scot responded to Johnson: “And that’s why England is known for her horses, and Scotland for her men!”
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