The COPPERHEAD RACER. Coelognathus radiatus
these attractive snakes are diurnal, ie they can be seen and active during the day. They can be quite large, but are not venomous or dangerous to humans in any way.
As always, lots more information about this and other snakes at our sister site www.hongkongsnakeid.com.
The following information is taken from there to explain the photo .
The Copperhead Racer will puff up their neck when threatened. The neck expands vertically making them look taller rather than displaying the notorious 'hood' seen on cobra species. A harmless defensive tactic but can be unsettling for the inexperienced. These snakes will almost always flee extremely quickly if they sense you approaching and despite a bite from a mature specimen being a bit painful they pose almost no danger to humans and have no venom. They have also been observed to play dead, rolling onto their back and opening their mount.