When I was planning for my last all day presentation I was considering the post lunch sleepiness that most audiences experience. I wanted to do something totally different that I knew would shock them out of their afternoon low. So I bought a muskrat trap.
I was talking about the "traps" AKA deep trouble you could get into by spam email marketing. I set the trap with great care. Then I put a pencil into the trap to set it off. The pencil snapped showing the trap to be real . . . This got their attention. I then reset the trap and talked about how learning what I was going to teach them in the next section would keep them from getting hurt in the email spam trap.
Then, with lots of suspense building as I approached the trap, I set it off with my bare hand, I let out a fake Karate-like scream, the trap slammed on my hand and I held it up hanging from my fingers. . . . Believe me this got their attention!
DO NOT TRY THIS! DO NOT TRY THIS! DO NOT TRY THIS!I know how to do this without getting hurt. I am not responsible if you break your finger or get hurt in any way !!!
There are many other ways to shock people. You could put a needle through a balloon, you could stick a knife through one of their coats. Stop by any magic or gag shop for tons of ideas. Just don't get too outrageous and scare people unnecessarily.