Rigging has got problem.

I didn't realise having a fat charactor could be so painful. I should have noticed and thought about why the tutuorial always use charactors thin like match sticks, because they are easy for rigging.
The weight on my penguin seems to need extra bones and joints to support. Or there's another way to do it, that is to creat a 'proxy geometry' to simplify the mesh. Then bind the skin to the proxy, parent proxy to the real geometry.