Place the egg in a cotton fabric. This is mainly for "egg safety" and for better results if you trying to find a hard boiled egg.
Now try to spin it.
Non boiled eggs are resist to spin. This caused not by the fabric fraction by the inertia phenomenon of the egg itself.
In the other hand boiled eggs are spinning since the are solid and no inertia is caused.
Hope you like it (and hopefully not knowing it yet!)