Answer:
What word is a plural, but when you add an "S" to the end, it becomes singular?
A nut cracker up in a tree.
I am a box that holds keys without locks, yet they can unlock your soul.
Two people are born at the same moment, but they don't have the same birthdays. How could this be?
White bird, featherless, flying out of paradise. Flying over sea and land. Dying in my hand.
This food is a tortilla filled with cheese and sometimes chicken before being heated or cooked.