Mommy told. Daddy takes one hour, for the one who wants to enter, to build his own door. Then he quickly slips inside, but that would only work if the structure is still alive. Using traditional heuristics, policemen can spot any dead volcano -- as long as it never decides to trap them in. Is there no other way out? Take the police as an example. In such occasion, the police will put you in prison or may return after one entire life-cycle.