An additional example of foreshadowing comes at the end of chapter 3 when Juana tells Kino that the pearl will ruin their son. Up until this moment there's been no sense that the pearl will be anything other than a huge stroke of luck for Kino and his family. Once they've sold this valuable, a much-sought-after object, they'll be able to swap their impoverished existence for a life of ease and comfort.
Tragically, that's not how things turn out. Juana is right to be suspicious of the pearl; she senses that it'll be much more trouble than it's worth. And this proves to be true. The doctor and his thugs try everything they can to steal the pearl instead if giving Kino a fair price for it. They hunt down Kino and his family like animals, and in the process Coyotito, Kino and Juana's son, is shot dead. Sadly, Juana was right after all.
It's also notable that Kino hears a song whenever something bad is about to happen. The song of the pearl gets stronger and stronger the nearer he gets to it. Of course, Kino doesn't yet know that the discovery of the pearl will bring him evil, but the song provides us with a further instance of foreshadowing—not to mention dramatic irony.