Learn Spanish (Latin America): Pensé que era una broma inofensiva, pero terminamos limpiando el piso. - I thought it was a harmless joke, but we ended up cleaning the floor.

In Spanish, to say you "ended up doing" something, you use terminar (or acabar) followed by the gerund (the -ando or -iendo form). So, terminamos limpiando means "we ended up cleaning." If you used the infinitive structure (terminamos de limpiar), the meaning would change completely to "we finished cleaning."

Why is Pensé in the preterite but era in the imperfect?

Pensé is in the preterite because it marks a specific, completed realization at that moment in the past. era is in the imperfect because it describes a characteristic or background state—the nature of the joke itself—without focusing on a specific beginning or end.

Could I use chiste instead of broma for "joke" here?

Probably not. Un chiste is typically a spoken joke with a punchline. Una broma is a practical joke or a prank. Since this joke resulted in a messy floor, it was definitely a prank!

Is terminamos in the present or the past tense here?