I mean when you register

    terra.creatureFactory.register({type: 'firstCreature'});

this is stored in the global `terra` variable... Would be better IMO

    var terra = new Terra();terra.creatureFactory.register({type: 'firstCreature'});

Actually, I've been thinking more about this and feel it's better to define creatures on the root terra object. Running the same simulation 100 times with slightly different starting conditions, for example, would require a new terrarium for each trial but creatures should be shared between..