Learn Spanish (Latin America): La rata entró a la casa y la mujer se echó a llorar. - The rat entered the house and the woman burst out crying.

The phrase echarse a followed by an infinitive is used to express that an action started very suddenly. On its own, llorar means to cry, but se echó a llorar means she suddenly burst into tears or burst out crying.

Why is it llorar instead of llorando if the English translation uses 'crying'?

In Spanish, the specific structure for this sudden action is echarse a + an infinitive verb. Even though we often say 'burst out crying' with an -ing word in English, Spanish requires the infinitive llorar after the preposition a.

I previously learned to use 'en' with this verb. Why does this sentence say entró a la casa?

In Latin America, it is much more common to use entrar a when talking about going into a physical place. In Spain, you will more frequently hear entrar en. Both are grammatically correct, but this sentence uses the typical Latin American preference.

Why are both entró and echó in the preterite tense instead of the imperfect?

Both actions are sudden, completed events that happen one right after the other: first the rat entered, then the woman immediately started crying. The preterite tense is used to narrate this kind of sequential chain reaction in the past.