An animal is often just a mirror of its owner’s state of mind. Thus, this book proposes that pets should be regarded as an instrument for psychological diagnostics in order to spot their owner's personal or an environmental deficiency. There are some cases in which animals clearly demonstrate abnormal behaviour, but this behaviour is secondary and caused by the owner's failure to build communication with the pet, judging its behaviour from the human perspective. The pet owner may say things like: "He is just taking revenge" or “He does it out of spite." The effectiveness of clinical behavioural medicine for animals could be significantly increased if the practitioners were able to do differential diagnostics of the "disordered links."