On the basis of seven incidents of panic in World War II which took place in the military, Marshall (1947: 145–146) offered the generalization that:

... It can be laid down as a rule that nothing is more likely to collapse a line of infantry in combat than the sight of a few of its number in full and unexplained flight to the rear ... That was how each of these seven incidents got its start. One or two or more men made a sudden run to the rear which others in the vicinity did not understand ... [I]n every case the testimony of all the witnesses clearly developed the fact that those who started the run ... had a legitimate or at least a reasonable excuse for the action.

Smelser (1963: 154) has analyzed such cases in the following way:

... the initial flight itself creates – as the remarks of Marshall show – a new set of necessary conditions for panic. To see someone running wildly is prima facie evidence that he is seeking to escape through limited exits (structural conduciveness), and that he is anxious. Furthermore, this observed flight is a precipitating event for the observer, and gives rise to the belief that something frightening is present, even though this “something” may not be identical to that which caused the original flight.

Smelser defines panic as “a collective flight based on a hysterical belief. Having accepted a belief about some generalized threat, people flee from established patterns of social interaction in order to preserve life, property or power from that threat!” (p. 131). His basic thesis can be reformatted into the proposition that flight occurs if an individual believes a) that a definite threat is present, and b) that escape routes leading away from the threat are limited or closing. When reformulated thus, the essentials of Smelser’s value-added theory are consistent with the ideas of several other recent theorists. For example, Fritz and Williams (1957), Quarantelli (1954), Janis et al. (1955), and Mintz (1951), all concur with Smelser that the two key factors leading to panic flight are: a belief that physical danger is present from which escape must be sought, and the belief that escape routes are either limited or closing. Janis and Leventhal (1968: 1061), for example, write:

It is this combination of cognitions, whether or not they are correct inferences about the subject situation, which is designated as “perceived entrapment,” and which is most likely to lead to wild flight, trampling of fellow victims, and other uncontrollable, distraught reactions of the type referred to as “panic.”

156We now proceed to a systematic review of the evidence concerning this theory. Definition Smelser’s definition of panic as “collective flight” is too restrictive since it does not include the range of behavior customarily associated with the term. Panic can be expressed in aggression or rage as well as flight, not to mention intense affiliative behavior. On the battlefield, panic can take the form of dashing about suicidally in front of enemy fire. The concept of panic also includes immobility (“freezing”) behavior, which is a not uncommon response to extreme terror. A theory of panic should make clear the conditions under which flight takes place rather than immobility, since both responses are possible when the individual is greatly threatened.