Answer:
A mechanism to discover who is following you.
They are toothy nocturnal immortals.
What is taken before you can get it?
When this is found in a road you are forced to make a decision.
Which weighs more? A pound of iron or a pound of feathers?
When is it bad luck to see a black cat?
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?