Bottle grenades are bottles that have the potental to explode, or have exploded, due to internal pressure. Bottle grenades are a phenomenon that occurs in wine making and homebrewing. There are a few causes for bottle grenades:

• There was too much priming sugar added to a bottled beverage. This is preventable. Use the right amount of sugar.
• Sparkling wine or beer was not bottled in pressure-safe bottles.
• A wine was bottled while it was still fermenting. The wine continued to ferment, producing CO2, and the bottles exploded. Put the wine under a traditional airlock, and watch it, or open bottles periodically to check for pressure.
• Sugar was added to an unstabilized wine and bottled. The sugar will ferment until the bottles explode. Don't let this happen.
• There was bacterial contamination. This is unlikely. Actually, I don't know if this is possible.