Learn French: La fille est toute fascinée par les rochers. - The girl is completely fascinated by the rocks.

Usually, adverbs never change their spelling. However, the adverb tout (meaning "completely" or "very") is a special exception! It changes to match feminine adjectives only if that adjective starts with a consonant or an aspirated 'h'. Because fascinée is feminine and starts with the consonant 'f', tout becomes toute.

If the girl was "completely amazed" (étonnée), would it still be toute?

No, it would be tout étonnée. The adverb tout stays invariable (spelled tout) before feminine adjectives that start with a vowel or a mute 'h'. The extra 'e' in toute fascinée is added purely to help with pronunciation before the consonant sound.

Why does fascinée end with an extra e?

Here, the past participle fasciné is being used as an adjective with the verb être (to be). Because it describes La fille, which is feminine and singular, it must agree by adding an extra e to become fascinée.

Why do we use par instead of de for "by"?

When expressing a state of mind or emotion in a passive sense, French often uses de (for example, aimé de tous - loved by all). However, fasciné is an exception that takes par, making it translate perfectly to the English "fascinated by".