Conversation so far:
When did Harry Houdini perform his buried alive stunt?
The first was in 1915.
Where did Harry Houdini perform his first buried alive stunt?
The first was near Santa Ana, California.
What did Harry Houdini's first buried alive stunt involve?
Harry Houdini was buried, without a casket, in a pit of earth six feet deep.
How did Harry Houdini escape his first buried alive stunt?
Harry Houdini became exhausted and panicked while trying to dig his way to the surface and called for help. He had to be pulled from the grave by his assistants.

Question: Why did he have to be pulled out?
Self-contained rewrite: Why did Harry Houdini have to be pulled out of his first buried alive stunt?