Bobby McFerrin took the stage at the first World Science Festival (2009) to demonstrate "expectations." The audience knew what note to hum based on what he did. It's a wonderful example of engagement.
In an interesting interview in the Guardian, McFerrin talks about another of his "engagements". He invites his audience to hum Ave Maria as he performs Bach's Prelude No. 1 in C major. He says "The numbers are in your favour. There will always be a few dozen people who know the tune to "Ave Maria", and others will join them. There was one gig in Paris when I could hear a few hundred people humming "Ave Maria"- and one amazing operatic tenor belting out over the top. Turns out that Plácido Domingo was in the audience. We put the hall lights up and I ended up duetting with him!"
Marney is the founder of Animatrix, an interactive consulting firm that has shipped over 300 projects in the last 25 years for companies that include Apple, BearingPoint, KPMG, Clinique, The Limited, AT&T, NewsCorp, The Walt Disney Company, The National Academy of Science and many others.
Marney.com is about interactive design- the creation of any experience that starts with the user. It can be a site, an ad, a toy, a place, an object.... anything that's designed for engagement.