i had 1 like that, would grab+ lock on but never try to kill them. Ithough the same that it would change after caught its 1st 1/2 dozen, but it never did was like it for 4 years . It never botherd me as long as he caught them, as you knew once he locked on (nothing) getting away. then i had another dog that would shake the shit out of them after it got bite few times, there all differnt this was late 80s
Spot on