The last time I made mead, some of the bottles spontaneously exploded. Either I need to refine the recipe, or procure stronger bottles...
Could have been it needed to ferment for a longer time and the yeast had not done a complete fermentation yet. Same thing happens to beer if the yeast is not allowed to do its job. A mead can take a while to ferment - 3-4 months in the primary and about the same time in a secondary.