Another impressive speech at the March For Our Lives was given by 9 year old Yolanda Renee King, granddaughter of that incomparable rhetorician, Martin Luther King. In her speech, she gets the crowd to collectively chant a series of phrases, and the way in which she encourages buy in, and hence enthusiasm, is masterful.
She first walks the crowd through the entire text, one phrase at a time. This is important. Nobody can chant with conviction if they are at odds with the message chanted. This is one reason many people (academic, for example) hesitate to join in chanting. The description of the Human Microphone in Chapter 2 of The Ground From Which We Speak discusses this important property of joint speech: it necessarily entails commitments. While speech done alone can be modified so that the utterer is not held directly responsible for the contents, joint speech commits the utterer. This is why joint speech is the usual form of an oath of allegiance, for example.
Having walked everyone through the text once, Yolanda does it two more times. Now the crowd can join in with vigour, for they are not wary about the text. Wonderful rhetoric from the young girl!