Jeff used an autoresponder (when you have trained the audience to respond with a specific answer) beautifully and absolutely worth mentioning:
First, he asked for permission. He asked the audience to respond with an energetic “ABSOLUTELY” whenever they were in agreement to a question he asked.
Second, he modeled the behavior by asking, “Can you do that?” while leaning forward with the expectation that the audience would respond with the correct answer.
Then, he reinforced the behavior. When he got a strong response, he acknowledged it. When it was rather wimpy (which it usually is the first or second time until the audience “gets it”), he would tease the audience into participating.
It then became “natural” for the audience to listen for and respond to a question with an energetic “Absolutely!”