Qual é a diferença entre I ONCE saw his sister, but I can't remember what she looked like. e I saw his sister ONCE, but I can't remember what she looked like. ?Podes indicar apenas respostas exemplo.

@Evan0999

There are three places where you could insert the word – once.

You have outlined two of them, both of which share the same meaning.

However, if you said – once I saw his sister… – This is quite different.

Once I tasted my first few drops of alcohol, I couldn’t stop wanting it.

Once I had been to the science laboratory, it was all I could talk about.

Once I saw his sister…. - The formation of the sentence implies that something radically changed for you after you had seen his sister.

However, the rest of your text tells us that this is not the case. So you absolutely cannot use the third form, because it changes the meaning, into a form which you cannot use.

This third form is not “casual“ or any such thing…