In court proceedings in the United States, a Perry Mason moment is said to have occurred whenever information is unexpectedly (to most present), and often dramatically, introduced into the record that changes the perception of the proceedings greatly and often influences the outcome. Often it takes the form of a witness's answer to a question, but it can sometimes come in the form of new evidence.
Perry Mason Moment:
In court proceedings in the United States, a Perry Mason moment is said to have occurred whenever information is unexpectedly (to most present), and often dramatically, introduced into the record that changes the perception of the proceedings greatly and often influences the outcome. Often it takes the form of a witness's answer to a question, but it can sometimes come in the form of new evidence.
https://en.wikipedia.org/wiki/Perry_Mason_moment