This is the amazing chrysalis of the Blue spotted crow butterfly.
The best way to spot them is out at night, like here, where their highly reflective surface shines bright in the torchlight. I have seen them on railings on the Peak and on Lung Fu Shan, and in more forested areas, under leaves, on a forest path. Always a wonder to behold, and very tricky to photograph, as it shines in the flash. I used a torch behind it to give it an outline, as well as off camera diffused flash for this.
And what comes out of this?
This lovely butterfly, the Blue-spotted Crow; with dark blue scales on the forewings, although they tend to keep them closed when they are feeding. This one in flight towards some daisies.
It has a slow flight, and I often find them in open fields.
You may have seen swarms of these sometimes on their favourite plants, maybe 30 or so on one bush, and as you get close they take off and flutter gently around you, a wonderful experience. see them at kadoorie farm, or Lions Nature Education Centre/park in Sai Kung.