You are in a closed room with no object made of metal, not even in your clothing.
You are given two iron rods, one of them is magnetic the other is not. How can you tell which one is magnetic?

Easy answer to this question is to suspend both the rods and see which aligns one particular way all the time.
Say the guy who locked you up, realized this. He also took away anything that you can suspend the rods with.

Now, how do you find which rod is magnetic?