Я заметил одну мелочь в отчёте.

I noticed one small detail in the report.

Breakdown of Я заметил одну мелочь в отчёте.

• я: I
• в: in
• заметить: to notice
• один: one

Questions & Answers about Я заметил одну мелочь в отчёте.

What does заметил tell me about tense and gender?

Заметил is past tense: noticed.

It also shows that the speaker is masculine. In Russian past tense, verbs agree in gender and number:

• я заметил = I noticed (spoken by a man)
• я заметила = I noticed (spoken by a woman)
• мы заметили = we noticed

So if a woman said this sentence, it would be:

• Я заметила одну мелочь в отчёте.

Why is it заметил and not замечал?

This is about aspect, which is very important in Russian.

• заметить → perfective
• замечать → imperfective

Я заметил... uses the perfective past, which means the action is seen as completed: at some point, I noticed it.

That fits this sentence well, because the speaker is talking about a specific result: they spotted one detail.

By contrast, я замечал would usually suggest something like:

• I used to notice
• I was noticing
• I had noticed on various occasions

So here заметил is the natural choice.

Why is it одну мелочь?