What turns Black Friday shoppers into raging hordes?

For the Black Friday faithful, the excitement begins on Thanksgiving, when eager shoppers line up outside big box and department stores for the chance to grab “doorbuster” sales and “prices slashed” merchandise when the doors open. Black Friday videos posted in recent years show shoppers shoving and shouting, with one temporary worker even trampled to death in 2008.

What turns ordinary shoppers into dangerous mobs?

Social scientists and psychologists are trying to find out.

Sharron Lennon, a professor in the merchandising programme at Indiana University, became interested in studying consumer misbehaviour after seeing news reports a few years back about fights breaking out