There are two Eggs on the center of your table.
You cannot figure it out which is boiled because there both look the same.
Can you find out which egg is boiled and which is not ?
the 2 eggs are not hot.
you cannot put it on the water.
you cannot weight it nor lift it to know which is heavier.
and most of all you cannot break the shell.
By How ?
Indeed that's the answer and is because the hardboiled egg (being a solid mass) has a higher angular moment of inertia than a raw egg (which has thick liquidy stuff in it). The hard-boiled egg spins for a longer time if both are rotated by applying the same torque.