behind closed doors

Have you ever wondered what goes on behind those closed/ locked doors?

Here is where the story starts….
5 girls were walking home after dinner on a chilly spring night
All of sudden they heard some knocking noise coming from the back of a locked door they had just walked past

A asked if any of them heard the sound
B said yes
C and D weren’t sure
E noticed there was light under the door and the main entrance of the store was half-closed

They froze there for a while, waiting for more signs
Just when they thought they heard it incorrectly, the knocking sound came back, less loud than the previous one
Looking at one another, each of them began to come up with their own speculations
Could it be that someone is trapped inside?
someone is moving stuff inside since it’s a storage(looks like it)?
Some spooky paranormal phenomena?
a naughty prank from some bored security guys?
the latest “American funniest video’’ or "You’ve been framed’’ shooting?

There was only one way to find out. The girls turned back and knocked on the door
Hello,anybody in there??

No answer

Seconds later, it knocked back

The girls knocked harder and increased their volume at the same time
Still, no answer.
The strange thing was every time they knocked, they heard the same knocking sound from the other side of the door almost right away although there was no one responding them

Curious and leery, A&B decided to drag another 3 people, F,G and H into their mini investigation

F,G and H reluctantly knocked on the door one by one,
Again, the knock echoed instantly
F presumed that it was the anti-theft device that mimicked knocking sound to create a sort of scarecrow effect while G and H chuckled at how the technology had just fooled 5 ingenuous girls who were clearly influenced by commercialized concepts of horror

Now the mystery solved. The girls continued their journey home but they couldn’t help wondering
The anti-theft system didn’t justify for the sound they all heard when there was no one knocking on it
So,
What if there was really someone being locked in there?
What if someone was trying to call for help but the door was soundproof which explained why only the pounding sound was heard?

Isn’t it disturbing???

P/S this story is a modified, partial work of ficiton. For original and unabridged version, please refer to Helen's blog :P:P