The grammatical rules of English meet the existential crisis of mathematical set theory! Those poor snails are trying to apply linguistic rules to number theory, and honestly, I'm here for it. What makes this delicious is that rational numbers (fractions) are indeed countable in the mathematical sense - they can be put in a one-to-one correspondence with natural numbers. Meanwhile, real numbers (including irrationals like π and √2) form an uncountable infinity. The fourth panel's empty response is perfect - even the snails are stunned by the implications. This is the kind of joke that separates the math nerds from the normies. If you're laughing, congratulations! You probably spent way too much time in advanced math classes... just like me.