She's a witch!
No I'm not!
There are ways to tell if she is a witch.
What do you do to witches?
And what do you burn apart from witches?
So why do witches burn?
...because they're made of wood?
Good, now how can we tell if she's made of wood?
BUILD A BRIDGE OUT OF HER!
Ah, but you can build bridges out of stone. Now does wood sink in water?
No! It floats! Throw her into the river!
What else floats?
Apples? Bread? A duck!
Right! So logically...
If she weighs the same as a duck....she's made of wood!