The defendant must believe, rightly or wrongly, that the attack is imminent.
"For some reason, the defendant believes his action was justified by his love of wild animals," he said.
The defendants and their supporters believe they know what it is.
She said the Government's ability to win cooperation agreements in the future might be damaged if defendants believed that they were not being treated fairly.
"The question is not just what the defendant believed, but what did he have a right to believe," Justice Crane said.
Whether to seek limits on a defense strategy that at least some black defendants believe to be helpful is a hard question for civil rights groups.
Did the defendant believe or claim what he was doing was right?
He added: "It goes to show that the defendant does not believe in the democratic system.
"The defendant must reasonably believe that there is no sure means of escape."