Good Riddles

Question: Until I am measured, I am not known. Yet how you miss me, When I have flown What am I?

Question: I am very strong and tough but can be broken in some ways. What am I?

Question: What sound do porcupines make when they kiss?

Question: What occurs once in a minute, twice in a moment and never in one thousand years?

Question: Poke your fingers in my eyes and I will open wide my jaws. Linen cloth, quills, or paper, my greedy lust devours them all.

What am I?