In this scene, Coyotito (Juana and Kino's son) is resting in his hanging box when suddenly a scorpion crawls down the rope. When Coyotito sees the scorpion he laughs and reaches for it, the scorpion falls landin on his shoulder and stinging him.
They then decide to bring Coyotito to see the doctor, even though the doctor belongs to another social class and its unlikely he will help them. Kino offers eight small pearls to the servant but it wasn't enough for the doctor to help them so Kino is turned away and the gates close.
The doctor has more important patients to care for.
Feeling discouraged, Kino and Juana decide to search for pearls of sufficient value. Kino cuts open one of the shells he found revealing the biggest pearl that either of them has ever seen.