Our Sheltie and our Jackie go at it sometimes, but only when they're inside. The Sheltie is about 12 years old and she's going to probably die soon, and the terrier is alpha, as is the Sheltie, so these are turf wars. :) The little one doesn't seem aggressive towards other dogs, nor even towards the Sheltie when they're outside the house.
I'll grant you that our terrier is DEFINITELY brainless, though. :)
Just one data point -- and the little boy is a rescue (we found him at my wife's school) so we're not sure he's 100% Jack.
It's possible, but that's a hard call to make unless you knew that dog.
I'll concede that that IS how it sounds, judging from the info that was posted.
Steve Sobol, Professional Geek ** Java/VB/VC/PHP/Perl ** Linux/*BSD/Windows Victorville, California PGP:0xE3AE35ED
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[TELECOM Digest Editor's Note: I've had a 'min pin' around here for a few months now. (Actually, the dog belongs to Raymond who stays here to look out for me.) I also have three female cats (all 'fixed'); the oldest (Missie) being four years old, Callie (because she is a calico) and Sassie are about three years old. The three cats put up with Willie, the minature pincher, who is alpha among them, but they tend to scream, squall and slap at him most days when he tries to boss them around too much. If any of the cats decides to sit on my lap, Willie gets insanely jealous. PAT]