Answer:
What does everyone know how to open but not how to close?
Sharp and long, flag of the world. What is it?
I have four wings but cannot fly. I never laugh and never cry. On the same spot always found, toiling away with little sound.
A mighty weapon in the war against winged household pests.
Dies half its life. Lives the rest. Dances without music. Breathes without breath.
If it’s information you seek, come and see me. If it’s pairs of letters you need, I have consecutively three. What am I?