Through observation, one realizes that there is usually fire at the source of smoke. Of course there are exceptions, such as in the case of the smoke bombs that immature high school students like to ignite in school in order to disrupt classes. These bombs trick the system. Schools, like most public buildings, have smoke detectors. Smoke detectors are supposed to alert people to the presence of fire, for where there is smoke, there is fire. In the case of smoke bombs, the alarms go off despite the absence of fire. There is another unusual circumstance that breaks the smoke-fire rule. Some fires, because of backdraft, appear to lack smoke. To better understand this phenomenon, it is useful to rent Backdraft, a good movie with the ever talented Kurt Russell. Yet, under normal circustances, one can still claim that where there is smoke, there is fire. This adage is usually not used to literally describe the relationship between fire and smoke. It is mostly used to point out that suspicious activity usually hides what one think it hides. For example, a woman might tell her friend that she suspects her husband of cheating because of the inordinately expensie gifts he gives his secretary. The friend might then reply, "Where there is smoke, there is fire." By this statemnt the friend affirms that indeed, he probably is cheating (just as 2/3 of married American men do cheat, according to recent statistics).