It is essential to assess the state of unconsciousness or consciousness of animals during slaughter. These assessments take place after the application of a stunning technique until the end of bleeding and during direct bleeding without stunning, until the end of bleeding. The indicators used are essentially similar for the different methods. However, the indicators are not all verified at the same times and their interpretation is not the same for all the methods either. This review describes the different brain circuits controlling the indicators of consciousness and unconsciousness, their interpretation and how they can be used for different slaughter methods. It also describes certain physiological reactions as well as specific points of vigilance for the different slaughter methods.