sorry it is slang..a dog that has too strong of a desire, very intent on the prey. in this case the bird. If a dog is too much you cant even get his attention to hold steady..his one goal is to race away after it until this is accomplished..no matter what..a more reasonable dog still knows you are beside him and will follow your instructions while keeping his goal of the bird..more managable i guess is a better choice..sorry.
I found a brit once and took it home..i could tell that several ribs had been broken at one time but this dog sure didn't act like it..they had healed however they were and he just never stopped running. I thought i had him secure in a side run but when i went inside to call he had dug his way out 9a matter of minutes) and raced away..that is a dog that is on the edge. He was rail thin and knew only one thing..to run, even tho he was terribly hot he didn't even stop to drink. Then there was little Samantha at the kennels. A pup of pure delight. I would set her on top of the trailer and back up a few steps clap my hands and she would just sail the air into my arms. I was able to back up quite a ways. Then she learned to flip as well. She was a beauty.