I have the opposite problem to you, i got my Jack Russell recently, he was about 3 1/2 when i got him, and i thought i was getting a nice friendly playful pet dog, the one that fetches sticks and balls in the park, and he`s not slightly interesting in playing at all, all he wants to do is kill things, anything he can get hold of, he can smell vermin from a long way off, the other night he went straight for a Hedgehog a hundred feet away in near pitch darkness, he has an unbelievable nose.
I do love him, but if someone offered me a JRT pup in exchange, i would be tempted ...