well there are a few methods for killing - put in a plastic bag and swing against a hard surface - or a really humane way involving dry ice- here is a link to one method-

http://www.alysion.org/euthanasia/index.html

here is discussion on this topic:
http://www.ball-pythons.net/index.ph...opic&p=674#674

Rats are not as smelly as mice from what I have read, and rats are WAY more intelligent.