This is the instinct most often understood and easily read. Prey instinct is one of the two most critical instincts necessary for excellent Schutzhund protection work. It is the second critical instinct for excellent Schutzhund protection work. It is characterized by a dog which demonstrates explosive, rhythmic barking in the out and holding phase of the protection work. It enables the dog to be positively stimulated into the work by compulsion.
Reactive aggression is totally different from active aggression.
It is not a critical instinct for Schutzhund training. It is characterized by a dog with a generally protective nature and is often linked to territoriality. Reactive aggression is commonly referred to as sharpness. However, reactive aggression must be delicately balanced in the dog's temperament because it is comprised greatly of both fight and flight instincts. Reactive aggression is only desirable if it is based on the fighting aspect with little or no trace of flight instinct being present.