to (someone's) amusement

Translations
к (чьему-то) удовольствию
To her amusement, the cat kept chasing its own tail.
К её удовольствию, кошка продолжала гоняться за своим хвостом.
Definitions
To (someone's) amusement refers to the state of finding something entertaining or funny, often resulting in laughter or enjoyment experienced by that person.