An Experiment

I conducted an experiment today.
I bought two bottles of drink and hung a bottle of drink in fornt of my scooter when I left.
It was like someone accidently forgot his/ her drink on the scooter.
I did it on purpose, though. 
I would like to how people are going to react to it and see if people are gonna leave it there or take it away.
After the first hald an hour, I retured from strolling around the nearby area.
The drink was still there.
However, after I attended the Japanese class, which lasted one and half an hours, surprisingly, it was gone!!!

What does this tell us?