Flash mobs initially involved dancing in the streets, freezing like statues or even giant pillow fights, but recently flash mob culture has begun to turn dangerous. Two weeks ago in Philadelphia, South Street was the scene of a flash mob gone bad. Foot traffic on the street changed in minutes from normal Saturday date night to an onslaught of mostly young people seemingly intent on destruction. Temple University professor Frank Farley said the difference with flash mobs is the speed at which they can be assembled, their size, and whether they have a purpose: "The biggest problem is the size. When anyone gets together and there is an unpredictability, uncertainty, and a strong thrill factor and a lot of arousal and excitement, sometimes it can spill over to the dark side."