Learn Hardcore Spanish (Spain): Mientras tanto, mi gato se esconde en el pasillo estrecho donde está la alfombra nueva. - Meanwhile, my cat hides in the narrow hallway where the new rug is.

Mientras tanto translates as “meanwhile” or “in the meantime”, and it’s used to introduce an action happening at the same time as another. It often stands alone at the start of a clause.
By contrast, Mientras by itself means “while” and functions as a conjunction directly linking two clauses, e.g. Mientras estudio, escucho música.

Why is the verb esconderse used here instead of just esconder?

In Spanish, esconderse is a pronominal verb (verb + reflexive pronoun se) that means “to hide oneself.”

Esconder alone is transitive (“to hide something”).
Esconderse (with se) makes it intransitive: mi gato se esconde → “my cat hides (itself).”

Why is the simple present tense se esconde used instead of a present continuous like se está escondiendo?

Spanish often uses the simple present to describe ongoing or habitual actions.

Se esconde can mean “he/she is hiding (right now)” or “he/she habitually hides.”
The continuous se está escondiendo is also correct but adds emphasis on the action in progress, which isn’t necessary here.

Why is the adjective estrecho placed after pasillo? Could it go before?

In Spanish, most adjectives follow the noun: pasillo estrecho (“narrow hallway”).
You can place estrecho before (estrecho pasillo) for stylistic effect or to emphasize the narrowness, but it sounds more poetic or formal.

Why is it en el pasillo estrecho and not en un pasillo estrecho?

The definite article el is used because we’re talking about a specific hallway (the one in the house).
Using un would suggest “in some narrow hallway,” as if unspecified or one of many unknown corridors.

Why is donde used to introduce the clause about the carpet, and could we use que or en el que instead?

Donde here is a relative adverb of place meaning “where.” It links back to pasillo estrecho:

…pasillo estrecho donde está la alfombra nueva = “the narrow hallway where the new carpet is.”
You could say …el pasillo estrecho en el que está la alfombra nueva, but that’s more wordy.

What does the relative adverb donde refer to in this sentence?

It refers to pasillo estrecho. In English: “my cat hides in the narrow hallway where the new carpet is.” The donde points back to the place already mentioned (the hallway).

What’s the difference between donde (no accent) and dónde (with an accent)?

donde (without accent) is a relative or declarative adverb meaning “where” (as in this sentence).
dónde (with accent) is an interrogative or exclamatory adverb meaning “where?”
Example:
– ¿Dónde está la alfombra? (“Where is the carpet?”)
– …pasillo donde está la alfombra (“hallway where the carpet is”).