鮮血直冒 The Tree Began To Bleed
原來八戒在外邊，聽見他們裡面嚷鬧，激得他心癢難撓，掣釘鈀，把一顆九叉楊樹鈀倒，使鈀築了幾下，築得那鮮血直冒，嚶嚶的似乎有聲。原来八戒在外边，听见他们里面嚷闹，激得他心痒难挠，掣钉钯，把一颗九叉杨树钯倒，使钯筑了几下，筑得那鲜血直冒，嘤嘤的似乎有声。
逐句解 Line by line
As it happened Bajie had been outside, and hearing the racket the two of them were making within, he got such an itch he could not scratch it; so he pulled out his muckrake, knocked over the nine-forked willow, gave it a few digs with the rake, and dug until fresh blood came spurting out and there seemed to be a thin whimpering sound.
心癢難撓 — an itch in the heart that cannot be scratched — is a real idiom for unbearable curiosity, and it is exactly right for a character told to stand still half a lǐ away while somebody else has a fight. Both 激得 and 築得 take de. 嚶嚶 is a sound word for something small and plaintive — birdsong, or crying. The tree is making it. 倒 is dǎo, to fall or be knocked over — not the dào of pouring.
This is one of the strangest images in the chapter and the novel offers no explanation for it. Bajie, bored, attacks a tree; the tree bleeds and whimpers. Nothing in the story requires this, and nothing afterwards refers back to it.
It is worth remembering that the willow was the cave's door, and that when the door opened the tree stopped existing. Whatever Bajie has knocked over and dug into is a tree that was, a few minutes ago, a piece of the fiend's magic. The novel lets the reader work that out and moves on.
The sound is what makes it land. Not a roar or a scream — a thin, small, plaintive noise, the kind a bird or a child makes. Bajie's response, in the very next line, is delight.