How can I tell whether an egg has been hard-boiled, through the shell? At my workplace, there's a mysterious carton of eggs in the common refrigerator. Nobody I've asked knows whether they're raw or cooked.

Is there a way to tell, without cracking one of the eggs open?
Take an egg from the carton and 'spin' it on the work counter. If it spins, it's cooked, if it does anything else, it's not.