FOUR RIDDLES

1. Why is a pig in a parlor like a house fire?
2. What do things run into and people run out of?
3. Why is St. Paul's Cathedral like a bird's nest?
4.  What is that which divides by uniting?

Answers:

1. The sooner it's put out, the better 
2. Money 
3. Because it was built by a Wren
4. Blades of a pair of scissors