How do inside animals get fleas?
Fleas commonly will hop on our trousers, and hitch a ride into our houses on us. Because our body temperature is much lower than dogs and cats, the flea usually jumps off of us as soon as it detects its mistake, and lurks in your carpeting and furnishings until your hapless dog or cat strolls by--and pounces. This is one of the reasons why year-round use of Sentinel (in dogs) and Revolution (in cats) is recommended--it is critical for prevention of "drive-by" flea festations!