the blue gill is sure older so hes smarter, the knife still young, and the long body make him harder to move ! usually, not many fish want to touch clown knife, even piranha, snake head !
I had the same thing happen when I tried to introduce a 4 inch African cichlid into the tank with my 4-5 inch Green Sunnies (Iwas rescuing the African and was actually worried about my Sunnies)!