What's the part of the story with Mama Elena seeing a spark of light land on Pedro?

From the text:

It was really a shame that as Tita was answering this question, saying that her secret was to prepare the mole with a lot of love, Pedro
happened to be nearby, and that they looked at each other for a fraction of a second like conspirators, remembering when Tita had been
bent over the grinding stone; for the eagle eye of Mama Elena saw the spark that flew between them from twenty feet away, and it troubled her deeply.