Some poor schmuck is committed to his or her eternal resting place, even though they aren’t quite ready to take that final dirt nap. Scratch marks are later found on the coffin lid along with other desperate signs of escape.
This not only happened, but back in the day it happened with alarming regularity. In the late 19th century, William Tebb tried to compile all the instances of premature burial from medical sources of the day. He managed to collect 219 cases of near-premature burial, 149 cases of actual premature burial and a dozen cases where dissection or embalming had begun on a not-yet-deceased body.
Now, this may seem ridiculous, but keep in mind this was an era before doctors such as the esteemed Dr. Gregory House gained the ability to solve any ailment within 42 minutes. If you went to the doctor with the flu in those days, he’d likely cover you in leeches and prescribe you heroin to suppress your cough. Their only method for determining if a person had died was to lean over their face and scream "WAKE UP" over and over again. If you didn't react, they buried you.