Nothing.
When audience reaction, energy and response is not at the level you were expecting, desiring or hoping for - soldier on. It does not mean they aren't enjoying themselves. For example, at corporate retreats your audience has probably been seated all day in the same room listening to lectures, keynotes, sales reports, etc. So do your homework. Find out what is happening before you go on and try to meet them at their level of interaction, interest and energy level. Be a professional. Maintain your own good attitude and enthusiasm during the show. And don't turn on your audience. You only have a short time to make a great impression.