Why do the ends of cans bulge out?

The ends of cans can bulge out due to the buildup of internal pressure, often caused by the fermentation of contents, temperature changes, or increased gas production from spoilage. When the pressure inside exceeds the structural integrity of the can, it causes the ends to bulge as a safety measure to prevent rupture. This bulging indicates that the can may no longer be safe to consume, as it could signal spoilage or contamination.