Re: Well, THAT was interesting....
Where I fish there are some HUGE snapping turtles. If you fish in the same spot for long enough, one might come and settle in front of you. They wait for you to drag the bluegills in and try to snag them as they go by. I also occasionally have big largemouth grab the bluegills once they are hooked.
When I was at college and FL, I used to see barracudas attach each other a lot. Sometimes you hook one and another goes after it, or sometimes you throw a small one back in and a large one attacks. Sometimes you put a large one in and one the same size attacks it while it rests. Vicious fish.