Re: What happens when you heat an object which is on fire in a microwave?

You're hunch about the "electricity" being related to ball lightning and 
plasma is correct.

One way to think about the operation of a microwave oven is that it's an 
"echo chamber" for an electric field.  The field is "tuned" to get water 
molecules jiggling back and forth and heat substances up via molecular 
"friction".

Plasma is a gaseous form of matter with an equal amount of positive and 
negative species (such as electrons and ions).  Plasmas are conductive, so 
when you lit the toothpicks, the hot gases around the flame were 
allowing local conduction of the electric field within the microwave 
chamber; you were locally "short circuiting" the field.  That's why you saw 
the glowing discharge or arcs around the flame.  You get the same "short 
circuiting" effect when you place a metallic object in the microwave; hence 
the warnings on certain packaging.

I hope your mom didn't catch you.  I'm not sure she'd buy the old "I'm 
experimenting with plasma physics" excuse.

Chris Seaman