How does the author introduce the superstitious nature of the characters in the first paragraph?

In the very first sentence Pelayo and his wife believed their son had developed a fever from the "stench" of crabs.

On the third day of rain they had killed so many crabs inside the house that Pelayo had to cross his drenched courtyard and throw them into the sea, because the newborn child had a temperature all night and they thought it was due to the stench.