The bystander effect

Not too long ago, I was watching a television show called "What would you do?" Its a hidden camera show that has actors perform different controversial scenarios in a busy area or restaurant to see how people would react to them when they thought no one was watching. One scenario that stood out to me as a perfect example of the bystander effect was when they had two actors, a man and a woman, portray as if they were on a first date at a bar. When the woman went to the bathroom, the male actor poured a powder into her drink in plain sight. Of course it was totally harmless but that was unknown to the bystanders, to them it appeared as if he was trying to drug her. The camera panned over the bar and it showed 4 different people looking at each other with shocked looks and shaking their heads but not one said anything to the woman when she returned and started sipping her drink. She even pretended to start to feel light-headed and still no one said anything. Although this situation wasn't real this is a perfect example to me because they all seen it and looked around at each other and didn't do anything because no one else said anything. At the end of the experiment the host interviewed one of the bystanders and asked why she didn't warn the woman and she simply said " No one else said anything, I didn't feel like it was my place."