Around
Easter, when we've
boiled up a few
dozen eggs for
colouring, someone accidently mixes the hard-boiled eggs with the
uncooked ones. This can be a sticky problem come the next morning, when
kiddies who expect
eggy goodness only get eggy
goo.
Anyway, to determine if that egg is cooked, all you have to do is lay the egg over on its side and spin it quickly. Let it spin for a few seconds, then using your fingertips, stop it and release. If the egg starts slowly spinning again, it is raw. This is because the liquid goo inside is still in motion, and when you stop and release it, the yolk causes the egg to return to spinning, albeit slowly.
If it stops and does not start spinning, it's cooked enough so the goo is not so gooey anymore.