A legal requirement on slaughter of livestock states that animals should be unconscious prior to the neck cut, with an exception for animals subjected to particular methods of slaughter prescribed by religious rites. Nevertheless, legislation states that unconsciousness should be ensured before the slaughter process is continued. Under practical conditions, assessing unconsciousness is based on absence of readily observable indicators (behavioural indicators and reflexes). There is no consensus, however, to what extent different behavioural indicators and reflexes accurately reflect unconsciousness. Merel Verhoeven has investigated in her PhD thesis what indicators accurately reflect unconsciousness during the slaughter process. For her research different livestock species (pigs, sheep and cattle) were subjected to different stunning and slaughter methods. Brain activity was measured continuously and linked to absence and presence of specific behavioural indicators and reflexes. The research shows that presence of rhythmic breathing, corneal reflex- and eyelid reflex do not necessarily indicate consciousness following slaughter without stunning. The absence of these indicators, on the other hand, are valid indicators of unconsciousness following stunning with carbon dioxide or following slaughter without stunning.