feline74:

If that's true, how come people can be exposed to second-hand smoke without becoming addicts?

In general, contrary to Hollywood, it's pretty hard to become a secondhand addict of anything. it doesn't work like in those movies where they kidnap you and "get you hooked on dope" by injecting you while you sit passively. it requires active stimulus-response-reward, where you provide the response.

that's kind of peripheral to the whole second hand smoke thing, though.