Answer:
What kind of table has no legs?
What can be measured but not seen?
I open wide and tight I shut, Sharp am I and paper-cut fingers too, so do take care, I'm good and bad, so best beware.
When it comes in, From sea to shore, Twenty paces you'll see, No less, no more.
A shimmering field that reaches far. Yet it has no tracks, And is crossed without paths.
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?