I respect barney’s thinking and all, but I believe the correct scientific methodology is as follows:

BEDEMIR:There are ways of telling whether she is a witch.
CROWD: Are there? What are they?
BEDEMIR: Tell me, what do you do with witches?
VILLAGER #2: Burn!
CROWD: Burn, burn them up!
BEDEMIR: And what do you burn apart from witches?
VILLAGER #1: More witches!
VILLAGER #2: Wood!
BEDEMIR: So, why do witches burn?
[pause]
VILLAGER #3: B–… ’cause they’re made of wood…?
BEDEMIR: Good!
CROWD: Oh yeah, yeah…
BEDEMIR: So, how do we tell whether she is made of wood?
VILLAGER #1: Build a bridge out of her.
BEDEMIR: Aah, but can you not also build bridges out of stone?
VILLAGER #2: Oh, yeah.
BEDEMIR: Does wood sink in water?
VILLAGER #1: No, no.
VILLAGER #2: It floats! It floats!
VILLAGER #1: Throw her into the pond!
CROWD: The pond!
BEDEMIR: What also floats in water?
VILLAGER #1: Bread!
VILLAGER #2: Apples!
VILLAGER #3: Very small rocks!
VILLAGER #1: Cider!
VILLAGER #2: Great gravy!
VILLAGER #1: Cherries!
VILLAGER #2: Mud!
VILLAGER #3: Churches — churches!
VILLAGER #2: Lead — lead!
ARTHUR: A duck.
CROWD: Oooh.
BEDEMIR: Exactly! So, logically…,
VILLAGER #1: If… she.. weighs the same as a duck, she’s made of wood.
BEDEMIR: And therefore–?
VILLAGER #1: A witch!
CROWD: A witch!

So, you see, the process is slightly more involved than Barney leads us to believe…