For at least the last 7,000 years, humans have extracted a mixture of enzymes from the stomachs of cows and sheep and goats and added it to milk. This causes the milk to curdle—it's part of the cheese-making process.
Oh, my God. - What's happened? - It's curdled, and it's got to go up in a minute. Oh, my Lord! - Ivy can manage it. Don't worry. Go on with what you're doing.
At the centre of the book is an unnamed Indian mother who makes dahi the traditional way, curdling each new pot of yogurt with a spoonful from the one before it.
When the thirsty travelers stopped for a drink and found their milk was now full of hard lumps, they drank it anyway and ate the curdled, cheesy leftovers.