I agree with what LANEY REECE says about squirrel dogs wholeheartedly, Ed.
Bloodline. Example: This is my wife's dog, although calling it "her's" angers me because I have to take care of the d@nged thing mostly. It could be called a feist, I guess, but most call it a rat terrier. Supposed to be natural squirrelers - HAH. Stupidest dog I have ever seen in my whole life. Will not come when called, and will try to bite me sometimes. Let loose off the leash it will run straight down to the middle of high traffic road and stand and sniff the pavement just waiting to get clobbered. Wont bark at strangers at the door, wont run after, or even acknowledge, squirrels when I take it to the woods, and - get this - it's scared of rabbits. When that thing passes I'm going to dance around it's grave.
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Bloodline is everything in squirrel dogs, not just breed.