Passive smoking, like the smoker, you are inhaling the fumes. Which by the way contain carbon monoxide. This is very dangerous, it acts by binding to your blood meaning that oxygen can't. This is why smokers have poor circulation and are tired. If you have carbon monoxide poisoning, you will be tired, feel sick, have head aches(serious) and eventually pass out and die. If oxygen can't bind to your blood, then you are slowly suffocating. As for the cancer, i presume its because as the carbon monoxide binds to your blood, it is also blocking your antibodies(found in blood) so your body cant fight infection very well. Which means if your infected with bacteria, they will continue to multiply and infect your cells.(Cancer) The lungs and throat are where the smoke passes and ends up.