Answer:
When a doctor hits you with a hammer he is testing this
Long and thin, red within, with a nail at the end.
You can't keep this until you have given it. What is it?
I am a king but also a common device of measure. What am I?
A mechanism to discover who is following you.
Lynn likes grapes but not potatoes. She likes squash but not lettuce, and she likes peas but not onions. Following the same rule, will she like pumpkins or apples?