You could fill them in any way you like. Look around you right now, this moment. What do you see? What do you smell.
If you don't smell anything, imagine something.
This can be fun.
Write two lines each starting with the words "I feel" using a physical sensation,
Write one line starting with the words "I feel" using an emotional response.
Do you understand this part? I feel uncomfortable because my eyes are rotting. I feel nervous, because I don't know if anyone can love a guy with rotten eyes.
;-)
Ha ha, just kidding, my eyes are not rotting. But you need to be a little crazy when you write poetry.