Determining which animals are sentient — capable of subjective experience — is both scientifically and ethically crucial. Researchers have developed a range of indicators to evaluate sentience across species.
Sentience assessment is not a binary yes/no determination but a continuum of evidence across multiple domains. Species that score highly on multiple independent indicators — nociception, learning, play, emotional complexity — warrant strong welfare protection. Species where evidence is emerging or contested deserve precautionary consideration. The expansion of sentience recognition to decapod crustaceans in UK law in 2022 illustrates how science can shift the boundaries of moral consideration. Welfare advocates should engage seriously with the scientific literature to ensure their claims about animal experience are evidence-based and current.