I am not about to try this.
The video is not very good quality but it does illustrate what happens.
Enjoy.
Edited to add a quote from the article:
“It's a crowd-pleasing party trick: Cut a grape in half, pop it in the microwave, hit "start" — then sit back and be dazzled by the grape balls of fire.”
Edited again to include the link
Oops. Here’s the link.