On Cheung Chau this afternoon, saw two big Rat Snakes wrestling.
Also known as a "dance", this is combat between two male snakes, fighting over breeding rights/territory. They rear up, push against each other, twist and push – in this case, at one point forming a circle.
The two broke off – maybe deciding I came too close – and moved off across the stream and into the trees. I reckoned each was around 3 metres long: large for this species.
Below is a video clip, showing the two snakes in action.