I recently saw a "Jackrat" When I asked what a "jackrat" was the owner said it was a cross between a jack russell and a rat "terrorist", her term for a rat terrier. Picture a jack, tricolor face but with the upright ears of the rat terrier although she did say the ears still flop over. She claims the mix with the rat terrier calms the dog down and they are much more sedate than a jack; that claim probably needs verification. Being a true mutt, they can come with the fuzzy face of the jack and sometimes only one ear stands up.