Bunny
Explanation
This is a short, punchy comic that plays on the gap between scientific facts and childhood innocence.
A parent is sitting with a small child and says: "Before I get into the details here, I want to remind you that all bunnies are 'coprophagic,' meaning they eat their own feces as part of the normal digestive process."
The bottom panel reveals the context: "I managed to soften the blow for the Easter Bunny conversation."
The joke works on multiple levels. First, there's the absurd inversion of expectations: the "difficult conversation" parents dread isn't telling children that the Easter Bunny isn't real -- it's informing them that real rabbits eat their own droppings (which is true; rabbits practice cecotrophy, re-ingesting special soft fecal pellets to extract additional nutrients).
Second, the parent's strategy of "softening the blow" is hilariously counterproductive. By leading with the disgusting biological fact about real rabbits, the parent presumably makes the child relieved to learn the Easter Bunny doesn't exist -- or at least reframes the disappointment. Learning that a beloved magical figure is fictional pales in comparison to learning it would have been a poop-eater.
The comic is characteristic of SMBC's style of finding humor in the intersection of scientific literacy and everyday life, particularly parenting.