My cockatoo, Spike has yet again chewed something. He has been chewing my refrigerator grate on and off for a few weeks every chance he gets. I try to keep an eye on him as I like to leave him out of his cage most of the time and he has a play pen perch and lots of toys. Yesterday I was putting a load of clothes in to wash and came in to find him in front of the fridge looking innocent. I got him back to his play pen and didn't think any more about it. Well, this morning I went to get a glass of ice water from the fridge door and cold water shot all over my legs and the floor. Apparently he had chewed through the water supply hose. Yelling at him only got me a pitiful, puzzled look. When he performs undesirable behaviour, how can I make him understand and associate his actions as bad?