Neighbours

I've witnessed some rather bizarre things in my apartment block but my new Chinese neighbours may have come up trumps. They have two flower pots outside their door, complete with two chopsticks rested across the top. Next to this arrangement they've sawn off the top of a 2 litre Pepsi bottle and placed it in front of the chopsticks. Every morning they then proceed to pour a cup of water into the Pepsi bottle. I have no idea why they are doing this. Any ideas? By the way, rumour has it that they'll shut down the university campus if they receive a single report of swine flu from the student population. So, volunteers for a martyr?