They're not that bad... None of my breeders are evil like that so it's not like they're "bad stock". I think that tub was just bored since I apparently forgot to give them chew toys after the last cleaning. Wood blocks are *vital* with raising ASFs. It's nice to see them turn a 2x2 into toothpicks instead of trying to escape.
I was just really amazed that they could chew through metal like that. I've seen them hanging on the top screen and trying to chew on it, but I always thought it was futile and just laughed at them.