The poisonous part of Crocodile's hook is very strong. It can kill a lot of people. What I am confused about is that he didn't use it in the Marineford War. He could have killed a lot of people with it and end it a lot quicker. I think this is a major plot hole and a lot of people would discuss about it in the future. It could be that the WG took off the poisonous part of Crocodile's hook, it is some kind of weakness in Crocodile that disabled his poison, or its a major plot hole.