I saw the original film in the 80s.  The dog's original owner paid black men
(specifically winos and the like) to beat the dog.  The dog began to
associate blacks with beatings.  When Kristi McNicol gets the dog she
discovers its history and attempts to reform the dog.  She hires a black
trainer who meets with success or so we assume until the final shot of the
film which leaves the viewer unsure of the trainers success.  Hope this helps.

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