合意同心 Of One Mind Together
怪道豬八戒跌了若干。似這般怎生是好？我師父與師弟卻又中了毒藥。這夥怪合意同心，卻不知是個甚來歷，待我還去問那土地神也。」怪道猪八戒跌了若干。似这般怎生是好？我师父与师弟却又中了毒药。这伙怪合意同心，却不知是个甚来历，待我还去问那土地神也。」
逐句解 Line by line
"No wonder Zhu Eight Rules took so many falls."
怪道 is "no wonder", the phrase for a penny dropping — literally "strange to say", but it has meant the opposite of strange for centuries. He is thinking back to the previous chapter, where Eight Rules met this same silk and went down repeatedly.
"What is to be done about a thing like this?"
怎生 is early vernacular for how, in what way — the same 怎生 as in the costume tag 你看他怎生打扮 much earlier. Here it is a real question and he has no answer.
"And my master and my brothers have been struck by poison on top of it."
中 is zhòng here, to be hit or struck — the reading in 中毒, to be poisoned, and 中彈, to be shot. Not the zhōng of middle or inside, which is the reading everywhere else in this chapter. 中原音韻 files the character in 東鍾 under both a level and a departing tone, which is the split we still have.
"This gang of monsters is of one mind together, and I still do not know what they are. I had better go and ask the local earth god again."
合意同心 — agreed in intent, one in heart — is what he has worked out and it is the important part: the Daoist and the spiders are not allies of convenience. 來歷 is provenance, background, what a thing actually is, and 甚 is shén, what. 土地 is the local earth god, the lowest rank of the celestial bureaucracy — a parish official with a parish official's knowledge.
Four short sentences of a man thinking on his feet, and the sequence is a diagnosis. No wonder Eight Rules kept falling — so this is what did it. What do I do about it? And my people are poisoned as well. Therefore: intelligence first.
The judgement in the middle is the sharp one. 合意同心 means he has understood that the abbey and the cave are one operation, not a poisoner who happened to have visitors. That changes the problem from a fight into a case, and it is why the next thing he does is not swing the cudgel.
And so he sends for the 土地. This is one of the running jokes and running truths of the novel: whenever Pilgrim needs to know what he is up against, he summons the local earth god — the most junior deity available, the one who actually lives there — and shakes the information out of him. It is exactly how you would find out who owns a strange house in a strange village. You ask the person whose parish it is.