Electrical and mechanical stunning before slaughter should render animals unconscious before killing — but failures occur regularly, causing conscious animals to enter the kill line.
Stunning failure means conscious animals experience the slaughter process — a welfare outcome of maximal severity. Even low failure rates across millions of animals represent enormous numbers experiencing preventable conscious suffering. Systemic improvements including CCTV monitoring, line speed limits, third-party auditing, and better equipment maintenance substantially reduce failure rates and the suffering they cause.