庚申齋 The Gengshen Fast
寡婦驚訝道：「官人們是長齋，是月齋？」行者道：「俱不是，我們喚做庚申齋。今朝乃是庚申日，當齋。寡妇惊讶道：「官人们是长斋，是月斋？」行者道：「俱不是，我们唤做庚申斋。今朝乃是庚申日，当斋。
逐句解 Line by line
The widow was taken aback: "Are you gentlemen on a lifelong fast, or a monthly one?"
She knows the categories, which tells you how ordinary lay fasting was. 長齋 with cháng is the permanent kind; 月齋 is the monthly one, kept on fixed days of each lunar month.
Pilgrim said: "Neither. Ours is what we call the gengshen fast.
This is a real observance and Pilgrim has picked the cleverest one available. The days of the calendar run in a cycle of sixty, each named by a pair of characters, and 庚申 is the fifty-seventh of them. Daoists held that on that night the three worms living inside the body climb out while you sleep to report your sins to heaven — so the devout stayed awake all night to stop them. ⚠ Those three worms come back at the end of this chapter, when the king wakes up and finds his head shaved.
Today happens to be a gengshen day, so we fast.
今朝 is zhāo, this morning, today — not the cháo that means the court or to face, which is the reading the same character takes five other times in this chapter.
The lie is perfect because it is true about the calendar and unverifiable about them. She can check that today is a gengshen day and cannot check whether these four keep the fast.
It also buys exactly the right amount of time. The gengshen vigil ends in the small hours — which is when Pilgrim intends to be up, dressed and out of the gates. He has chosen an observance whose schedule is his escape plan.