The Comfortis website has great information pages that explain the life cycle of a flea as well as the best methods for killing the fleas in your home. If you have an infestation and you're only treating your pet, you're only treating one out of four life cycles of the flea population in your house! A link to the Comfortis website is below...
Comfortis Flea Life Cycle Page
Comfortis Controlling Fleas in Your Home