Estimated at two metres long. Immobile in vegetation at (human) head height. I was focused on looking for birds' nests and only noticed the snake when I was less than two metres from it! It vibrated the tip of its tail gently, either as a warning or as a way to express tension. I initially thought it had just swallowed some prey, but when I moved away it deflated its throat, and when I moved closer again it inflated it again - so it was a defensive/threat posture.