Learn Croatian: Naime, vruća površina stvara fatamorganu. - Namely, the hot surface creates a mirage.

When naime acts as an explanatory discourse marker (meaning "you see" or "in fact") at the very start of a sentence, it sets up the entire following clause as an explanation for a previous statement. In this sentence-initial position, it is standard grammar to separate it with a comma.

If I wanted to put naime in the second position, how would this sentence change?

You could move it to the second position, making the sentence Vruća površina naime stvara fatamorganu. Notice that when it shifts into this position after the first phrase, the comma is typically dropped. This makes the flow slightly smoother while keeping the exact same "explanatory" meaning.

Why use the imperfective verb stvara here instead of its perfective pair stvori?

We use the imperfective stvarati because this sentence describes a general, continuous phenomenon or a scientific fact. A hot surface continuously or repeatedly creates a mirage. If you were talking about a single, sudden event that just finished, you would use the perfective stvori.

The word fatamorganu is clearly a loanword. Does it follow standard Croatian noun rules?