Learn Spanish (Latin America): Se le arrugó el pantalón al sentarse encima de la cama. - His pants got wrinkled when he sat on top of the bed.

This uses the accidental se structure, which removes the active blame from the person. Instead of saying he actively wrinkled them, the structure se + indirect object pronoun (le) + verb (arrugó) translates roughly to 'the pants wrinkled themselves to him.' It highlights that it was completely involuntary.

The translation says 'his pants', but I don't see sus pantalones in the Spanish sentence. How does that work?

In Spanish, when talking about clothing or body parts involved in an action, we typically use the definite article (el or la) instead of a possessive adjective like sus. The indirect object pronoun le already tells us who was affected by the wrinkling (him), making sus redundant.

Why is pantalón singular here when the English translation says 'pants'?

In Spanish, you can use either the singular el pantalón or the plural los pantalones to refer to a single pair of pants. Both are correct and widely used, but since el pantalón is singular here, the verb arrugó must also be singular to match it as the subject of the clause.

Why does the sentence use al sentarse instead of cuando se sentó?