Today, took my wife's bicycle to repair place, after the second mysterious puncture in the space of a few weeks.
She had left her bike near the Praya, while heading for work; came back to find the front tyre completely flat.
Bicycle Repair Man (a top man, works near King's Cafe) saw the flat tyre, and immediately told me it must be a "nervous" woman who has evidently started a habit of puncturing tyres of bikes left near the ferry pier. He had another eight or so bikes awaiting puncture repairs; told me if I checked near the pier, could see many bikes with flat tyres.
With inner tube removed, there too was typical hole he'd been finding: small, as if by something sharp and round like a needle. One bike awaiting puncture repair belonged to a woman who had seen Crazy Bike Puncture Woman in act of stabbing her tyre - but not in time to catch her.
Evidently, the puncture habit started around Chinese New Year. No fixed time of day for puncturing.
So, if you have a bike on Cheung Chau, take care - and keep an eye out for Crazy Bike Puncture Woman!