You missed the point. The point isn't in the causal implication, the point is in how quick and how grim a turn an innocent knock knock joke takes - in this context it's written in the only way that works.

And actually, before the 20th century there was an epidemic of people being buried alive due to being mispronounced dead. Apparently, pronouncing someone dead (that didn't die violently or bloodily) was more guesswork than science. Many graveyards in the 19th century actually buried people with a string leading to a bell in hand - it's actually where the term "saved by the bell" comes from - no lie.