Both human animals and non-human animals are gifted with a nervous system, more or less developed, which allows them to feel and be conscious of their environment and to be able to distinguish what is pleasurable, dangerous, aggressive and painful, (writes Vasco Reis)
These beings all experience sensations, emotions and feelings in a similar manner. This being the case they can use the mechanisms of fight and flight, without which, they would not be able to survive. Therefore fear and pain are essential for survival.