The human-animal line was drawn at awareness of punishment.

Evidence

A sharp distinction could thus be made between humans and animals. Only the former had an awareness that punishment was attached to the violation of a moral or legal rule—including an active right—hence only humans could have natural rights. Conversely, only subjects who possessed rights could be regarded as human. — Talal Asad, Formations of the Secular, 635

Categorization

• BMF: The idea that to be human is to grasp that punishment attends violation evokes the legal logic of We (Zamyatin) where the One State’s punishment apparatus defines and enforces what counts as rational personhood.
• XREF: connects to: In folklore, becoming an animal is universally understood as a punishment; Raising a child requires governing an existence at once animal-like and human. — Simone de Beauvoir, The Second Sex, 1518