BANG!
Like it had hit a wall, the snake's head was stopped by the sword. The snake was long, but it wasn't incredibly massive. Its head was barely half a meter across.
Because of that, Shang was able to block the snake's head with his sword.
To paint a clearer picture, one only needed to imagine an attacking dog. The dog bit forward, but the human in front of it took a long stick and held it vertically, pushing it back. Since the dog's head was in its normal position, its mouth couldn't open wide enough to get the entire length of the stick into its mouth. Sure, if the stick were horizontal, it wouldn't be a problem.
Shang's arms shook under the weight, but the snake hadn't put its full power behind its bite. After all, it still had to keep an eye out for the green bird.
Because of that, Shang managed to keep his sword relatively straight.
When the snake's snout hit the blade, it began to bleed. The wound wasn't deep, but it had drawn blood.