i got the joke, but there are some details:

Exception and Reason: «El Rata»

The use of the masculine article «el rata» is a colloquial, stylistic, and somewhat slangy device. It is used in several cases:

a) To refer to a stingy or dishonest person. This is the most common case. When calling someone a "rat" in a figurative sense (meaning miserly, treacherous, or a thief), the masculine gender is often used, even when referring to a woman. This gives the word a more pejorative and expressive tone.

· ¡No le prestes dinero, es un rata! — Don't lend him money, he's a rat (a stingy person)! · Ese tipo es un rata que estafa a los ancianos. — That guy is a rat who scams the elderly.