It's a closely guarded secret, but big-time filmmaking is all about reusing existing resources. Think of all the valuable rehearsal time you could save, for example, by casting Samuel L. Jackson as a tougher-than-leather federal agent and Eugene Levy as the nebbishy dental-supplies salesman who stumbles into his custody. Those guys can play roles like that in their sleep, right? Now – and here comes the important part – you just have to remember to give either of them something remotely funny to do or say. Clarifying note: Uncontrollable flatulence ceased to count as "funny" more than a decade ago.