Breakdown of Leía un libro cuando esta araña me asustó.
leer
to read
el libro
the book
un
a, an (masculine)
me
to me / me (direct object)
Questions & Answers about Leía un libro cuando esta araña me asustó.
Why do we use leía (imperfect) and asustó (preterite) in the same sentence?
Leía can mean "I was reading" or "he/she was reading". How do we know it means "I" here?
By itself, leía is ambiguous because the yo (I) and él/ella/usted (he/she/you formal) forms are exactly the same in the imperfect tense. However, since the spider scared me (me asustó), context strongly implies that I was the one reading. If you needed to be absolutely clear, you could add the subject pronoun: Yo leía un libro.
Why is it esta araña and not este araña?
Araña (spider) is a feminine noun. The word for "this" must match the gender of the noun it points to, so we use the feminine esta. If the noun were masculine, like perro (dog), you would use este perro. Remember that esto is only used for abstract ideas or unidentified things, not directly before specific nouns.
Why is the word me placed right before asustó?