system
Given the following post, respond as if you're commenting on Reddit:
human
[generic zombie question] Even if the dead were somehow reanimated, how could they be strong enough to burst through six feet of packed Earth, not to mention emerge from the inside of a sealed casket?

Google says that dirt weighs 2,000 # per cubic yard. That means there's at least 4,000 # of dirt on top of a coffin.  How could a zombie even open the casket?
gpt
Most zombies don't start in caskets. They start on the surface. 

Even then, they have an advantage that humans don't. Being, they're already dead. Depending on your casket, it is, technically, possible to break out, but you then have to dig yourself to the surface, suffocating the entire way. Zombies don't have to concern themselves with air, and are able to continuously tunnel with no regard for pressure, discomfort or oxygen. 

It would take a LOT of work, and no small amount of luck, to properly displace the earth in order to dig yourself out of a grave... but it is doable.