Answer:
What word is a plural, but when you add an "S" to the end, it becomes singular?
My life can be measured in hours, I serve by being devoured. Thin, I am quick. Fat, I am slow. Wind is my foe.
There are 30 cows and 28 chickens. How many didn't?
What can be heard and caught but never seen?
I am the yellow hem of the sea's blue skirt.
I am a cave full of bones and the house of a worm.