"It's much easier to build an AI system to detect a nipple than it is to detect hate speech," he said.

It shouldn't be a surprise that Facebook's AI can spot nipples given the platform's history of banning, then begrudgingly allowing, breastfeeding and nudity in iconic photos. (Though it still doesn't let folks #freethenipple on Instagram.) But Facebook has outlined practical reasons for why its AI should be combing the platform for nipples. Its adult and nudity policy lists all the content the platform removes by default -- not just for users more sensitive to sexual imagery, but to prevent the sharing of content depicting non-consensual acts or underage people.