Went out last night to check the water with my dying torch and saw a dangerous looking snake slithering up my drive. You mentioned something about them getting active when there's a break from a few days rain - it was just like that. Hard to say what it was - can't readily identify it from the Snakes of Taiwan website - actually looked a bit like the Chinese Mountain snake that you mentioned but it says they only grow to 40cm and i think it was about 70 cm. Possibly a habu but the head seemed a bit smaller. Tried to take a pic but my camera was acting up. Will check my camera later to see if anything came out.