Prison Science - What's the Difference Between Prison Science and Research Subjects?

Zimbardo says they could left at any time, but like, all they were so into their rolls. And another very important thing about the payment is that you don't get paid until the end. Yead an incentive to stay on as long as possible. So simbardo now says he's like, if they said, i quit the experiment hereby then i would have let them leave. But there's no evidence that he ever communicated that to any of them. This is weird to me.